Microhard Systems 01P6 900 MHz Spead Spectrum Module User Manual MHX920Emanua

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Operating Manual
MHX-920E
900 MHz Spread Spectrum OEM Transceiver
Revision 1.00 March 6, 2001
Microhard Systems Inc.
#110, 1144 - 29th Ave. N.E.
Calgary, Alberta T2E 7P1
Phone: (403) 248-0028
Fax: (403) 248-2762
www.microhardcorp.com
MHX-920E
900 MHz
Spread-Spectrum
Embedded Modem
WARNING
In order to comply with the FCC/IC
adopted RF exposure requirements, this
transmitter system will be installed by the
manufacturer's reseller professional.
Installation of all antennas must be
performed in a manner that will provide at
least 23 cm clearance from the front
radiating aperture, to any user or member
of the public.
This manual contains information of proprietary interest to
Microhard Systems Inc. It has been supplied in confidence to
purchasers and users of the MHX-920E, and by accepting this
material the recipient agrees that the contents will not be copied
or reproduced, in whole or in part, without prior written consent
of Microhard Systems Inc.
Microhard Systems Inc. has made every effort to assure that this
document is accurate and complete. However, the company
reserves the right to make changes or enhancements to the
manual and/or the product described herein at any time and
without notice. Furthermore, Microhard Systems Inc. assumes
no liability resulting from any omissions in this document, or
out of the application or use of the device described herein.
Microhard Systems’ products are appropriate for home, office,
or industrial use, but are not authorized for utilization in
applications where failure could result in damage to property or
human injury or loss of life.
The electronic equipment described in this manual generates,
uses, and radiates radio frequency energy. Operation of this
equipment in a residential area may cause radio interference, in
which case the user, at his own expense, will be required to take
whatever measures necessary to correct the interference.
FCC Declaration of Conformity
EQUIPMENT LABELING
The manufacturer, product name, and FCC
and Industry Canada identifiers of this
product must appear on the outside label of
the end-user equipment.
This device complies with Part 15 of the FCC Rules.
Operation is subject to the following two conditions: (1) this
device may not cause harmful interference, and (2) this
device must accept any interference received including
interference that may caused undesired operation.
Microhard Systems Inc.’s products are warranted against all
failures which occur as a result of defective material or
workmanship within 12 months of purchase by the user. This
warranty does not extend to products that, in the opinion of
Microhard Systems Inc., have been subject to misuse, accidents,
lightning strikes, improper installation or application, nor shall
it extend to units which have, in Microhard Systems Inc.’s
opinion, been opened, tampered with or repaired by an
unauthorized facility.
Microhard Systems Inc.
Leaders in Wireless Telecom
th
#110, 1144 - 29 Ave. N.E.
Calgary, Alberta T2E 7P1
Phone: (403) 248-0028
Fax: (403) 248-2762
www.microhardcorp.com
ii
© 2001 by Microhard Systems Inc., All Rights Reserved.
HyperTerminal is copyrighted by Hilgraeve Inc, and developed for Microsoft.
Microsoft and Windows are registered trademarks of Microsoft Corporation.
pcANYWHERE and Symantec are registered trademarks of Symantec Corp.
All other products mentioned in this document are trademarks or registered
trademarks of their respective holders.
Manual Revision 1.00, March 6, 2001.
MHX-920E Operating Manual
Contents
1.
2.
3.
4.
iii
Introduction
1.0
Product Overview .............................................................................................................................................................................. 1
1.1
Features.............................................................................................................................................................................................. 1
1.2
About this Manual ............................................................................................................................................................................. 2
Electrical/Physical
2.0
Functional Block Diagram ................................................................................................................................................................. 3
2.1
Pinout................................................................................................................................................................................................. 4
2.2
LED Operation................................................................................................................................................................................... 6
2.3
DC Characteristics ............................................................................................................................................................................. 8
2.4
AC Characteristics .............................................................................................................................................................................. 9
Modes of Operation ..................................................................................................................................................................................... 11
3.1
Data Mode ........................................................................................................................................................................................ 11
3.2
Command Mode ............................................................................................................................................................................... 12
3.2.1 AT Command Interface ....................................................................................................................................................... 13
3.3
Switching Between Command and Data Modes ............................................................................................................................... 13
Configuration
4.1
Quick Start Approach ...................................................................................................................................................................... 15
4.2
AT Commands................................................................................................................................................................................. 16
A - Answer........................................................................................................................................................................................ 17
E - Command Echo.......................................................................................................................................................................... 17
I - Identification ............................................................................................................................................................................... 17
O - Online Mode .............................................................................................................................................................................. 17
Q - Quiet Mode................................................................................................................................................................................ 17
V - Result Codes Display................................................................................................................................................................. 17
W - Connection Result..................................................................................................................................................................... 18
Z - Reset Modem and load stored configuration .............................................................................................................................. 18
&C - DCD (Data Carrier Detect) ..................................................................................................................................................... 18
&D - DTR (Data Terminal Ready)................................................................................................................................................... 18
&F - Load Factory default configuration ......................................................................................................................................... 18
&K - Handshaking ............................................................................................................................................................................ 18
&S - DSR (Data Set Ready)............................................................................................................................................................. 19
&V - View Configuration ................................................................................................................................................................. 19
&E - Framing Error Check................................................................................................................................................................ 19
&W - Write Configuration to memory ............................................................................................................................................. 19
Sxxx? - Read S register value........................................................................................................................................................... 19
Sxxx=yyy - Set S register value ....................................................................................................................................................... 19
Command Result Codes................................................................................................................................................................... 20
4.3
S Registers ....................................................................................................................................................................................... 21
S Register 2 - Escape Code ............................................................................................................................................................... 21
S Register 3 - CR Control Code....................................................................................................................................................... 21
S Register 4 - Linefeed Control Code .............................................................................................................................................. 21
S Register 5 - Backspace Control Code ........................................................................................................................................... 21
S Register 101 - Operating Mode..................................................................................................................................................... 22
S Register 102 - Serial Baud Rate.................................................................................................................................................... 24
S Register 103 - Wireless Link Rate ................................................................................................................................................ 24
S Register 104 - Network Address ................................................................................................................................................... 25
S Register 105 - Unit Address.......................................................................................................................................................... 25
S Register 106 - Primary Hopping Pattern ....................................................................................................................................... 25
S Register 206 - Secondary Hopping Pattern .................................................................................................................................... 25
S Register 107 - Encryption Key...................................................................................................................................................... 27
S Register 108 - Output Power Level............................................................................................................................................... 27
S Register 109 - Hopping Interval.................................................................................................................................................... 28
S Register 110 - Data Format............................................................................................................................................................ 29
S Register 111 - Packet Minimum Size ............................................................................................................................................ 29
S Register 112 - Packet Maximum Size............................................................................................................................................ 29
S Register 114 - Packet Size Control ................................................................................................................................................ 29
S Register 116 - Packet Character Timeout ...................................................................................................................................... 29
S Register 113 - Packet Retransmissions .......................................................................................................................................... 30
S Register 213 - Packet Retry Limit.................................................................................................................................................. 31
S Register 115 - Packet Repeat Interval........................................................................................................................................... 31
S Register 117 - Modbus Mode ........................................................................................................................................................ 32
S Register 118 - Roaming ................................................................................................................................................................. 33
S Register 119 - Quick Enter to Command....................................................................................................................................... 33
MHX-920E Operating Manual
A.
B.
C.
D.
F.
G.
H.
I.
S Register 120 - RTS/DCD Framing................................................................................................................................................. 33
S Register 121 - DCD Timeout......................................................................................................................................................... 33
S Register 122 - Remote Control ...................................................................................................................................................... 34
S Register 123 - RSSI Reading ......................................................................................................................................................... 34
4.4
Diagnostics, Statistics and Remote Control ...................................................................................................................................... 35
4.4.1 Spectrum Analyzer Feature ............................................................................................................................................................... 35
4.4.2 Statistics............................................................................................................................................................................................ 35
4.4.3 Remote Control and Diagnostics ...................................................................................................................................................... 36
Installation ................................................................................................................................................................................................... 39
5.1
Estimating the Gain Margin.............................................................................................................................................................. 39
5.2
Antennas and Cabling....................................................................................................................................................................... 41
5.2.1 Internal Cabling ................................................................................................................................................................................ 41
5.2.2 Installing External Cables, Antennas and Lightning Arrestors.......................................................................................................... 42
Modem Command Summary ...................................................................................................................................................................... 45
Serial Interface ............................................................................................................................................................................................ 47
Sample Schematic Diagram ........................................................................................................................................................................ 49
Factory Default Settings.............................................................................................................................................................................. 51
Performance Tables...................................................................................................................................................................................... 53
Hopping Tables............................................................................................................................................................................................ 55
Technical Specifications ............................................................................................................................................................................. 57
Mechanical Drawing.................................................................................................................................................................................... 59
Glossary ...................................................................................................................................................................................................... 61
iv
MHX-920E Operating Manual
5.
1. Introduction
1.0 Product Overview
The MHX-920E is a high-performance embedded wireless data transceiver.
Operating in the 902 - 928 MHz ISM band, this frequency-hopping spreadspectrum module is capable of providing reliable wireless data transfer
between almost any type of equipment which uses an asynchronous serial
interface. The small-size and superior RF performance of this module make
it ideal for many applications. Typical uses for this module include:
SCADA
Traffic Control
Remote Monitoring
Fleet Management;
Telemetry;
Remote Camera/Robot Control;
Security Systems; and,
Display Signs.
While a pair of MHX-920E modules can link two terminal devices (“pointto-point” operation), multiple modules can be used together to create a
network of various topologies, including “point-to-multipoint” and “repeater”
operation. Multiple independent networks can operate concurrently, so it is
possible for unrelated communications to take place in the same or a nearby
area without sacrificing privacy or reliability.
1.1 Features
Key features of the MHX-920E include:
n transmission within a public, license-exempt band of the radio
spectrum1 – this means that it can be used without access fees
(such as those incurred by cellular airtime);
n a serial I/O data port with handshaking and hardware flow
control, allowing the MHX-920E to interface directly to any
equipment with an asynchronous serial interface.
902-928 MHz, which is license-free within North America; may need to be factory-configured
differently for some countries.
MHX-920E Operating Manual: Chapter 1 Introduction.
n 64 sets of user-selectable pseudo-random hopping patterns,
intelligently designed to offer the possibility of separately
operating multiple networks while providing security, reliability
and high tolerance to interference;
n encryption key with 65536 user-selectable values to maximize
security and privacy of communications;
n built-in CRC-16 error detection and auto re-transmit to provide
100% accuracy and reliability of data;
n ease of installation and use – the MHX-920E module uses a
subset of standard AT style commands, very similar to those
used by traditional telephone line modems.
While the typical application for the MHX-920E is to provide a short- to
mid-range wireless communications link between DTEs, it can be adapted to
almost any situation where an asynchronous serial interface is used and data
intercommunication is required.
1.2 About this Manual
This manual has been provided as a guide and reference for installing and
using MHX-920E wireless modem modules.
The manual contains
instructions, suggestions, and information which will help you set up and
achieve optimal performance from your equipment using the MHX-920E
module.
It is assumed that users of the MHX-920E module have either system
integration or system design experience.
Chapter 2 details the
electrical/physical attributes of the module. Chapter 3 explains the different
modes of operation. Chapter 4 provides complete details of all configuration
parameters; and, Chapter 5 is an installation/deployment guide. The
Appendices, including the Glossary of Terms, are provided as informational
references which you may find useful throughout the use of this manual as
well as during the operation of the wireless modem.
Throughout the manual, you will encounter not only illustrations that further
elaborate on the accompanying text, but also several symbols which you
should be attentive to:
Caution or Warning: Usually advises against some action which could
result in undesired or detrimental consequences.
Point to Remember: Highlights a key feature, point, or step which is worth
noting, Keeping these in mind will make using the MHX-920E more
useful or easier to use.
Tip: An idea or suggestion is provided to improve efficiency or to make
something more useful.
With that in mind, enjoy extending the boundaries of your communications
with the MHX-920E module.
MHX-920E Operating Manual: Chapter 1 Introduction
2. Electrical/Physical
2.0 Functional Block Diagram
DVcc
AVcc
Mixer
LNA
Antenna
Switch
IF Demod
GND
- +
Frequency
Synthesizer
Comparator
Mixer
PA
GAIN
RSSI1-3
\Config
\Reset
RXMODE
TXMODE
uC
A/D
SRAM
EEPROM
8 bit data bus
TxD
RTS
DTR
UART
(DCE)
RxD
CTS
DSR
DCD
Figure 1. Functional Block Diagram
MHX-920E Operating Manual: Chapter 2 Electrical/Physical
2.1 Pinout
Figure 2 provides a top-view pinout drawing of the MHX-920E module. The
corner pins (1,20,21,40) are labeled directly on the module.
AVcc
AVcc
DVcc
DVcc
DVcc
DVcc
DVcc
NC
\Config
\Reset
GND
GND
GND
GND
GND
GND
GND
NC
NC
NC
10
11
12
13
14
15
16
17
18
19
20
MHX-910
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
NC
NC
NC
NC
NC
NC
NC
Rx/SYNC
TxMODE
RSSI3
RSSI2
RSSI1
CTS
RTS
DSR
NC
DTR
TxD
RxD
DCD
Figure 2 - Pinout (Top View)
Table 1. Pin Description
Pin Name
No.
Description
I/O
AVcc
1,2
Positive Supply for Radio Circuitry. See Section
2.3 for DC Characteristics
\Config
Leave unconnected. For factory use only. Do
not ground
CTS
28
RS-232 Clear to Send. Active low (TTL level)
output. See Appendix B for a complete description
of all RS-232 signals.
DCD
21
RS-232 Data Carrier Detect. Active low (TTL
level) output.
DSR
26
RS-232 Data Set Ready. Active low (TTL level)
output.
DTR
24
RS-232 Data Terminal Ready. Active low
(TTL level) input.
DVcc
3-7
Positive Supply for Logic circuitry and I/O
pins. See Section 2.3 for DC Characteristics
MHX-920E Operating Manual: Chapter 2 Electrical/Physical
Table 1 (continued)
GND
11-17
Ground reference for logic, radio and I/O pins.
\Reset
10
Active low reset input to the module. See
Section 2.4 for timing information.
RSSI1
29
Receive Signal Strength Indicator 1. This
output is the first of the three RSSI indicators
to become active high as the signal strength
increases. See Section 2.2 for details
RSSI2
30
Receive Signal Strength Indicator 2. This
output is the second RSSI indicator to become
active high as the signal strength increases.
See Section 2.2 for details.
RSSI3
31
Receive Signal Strength Indicator 3. This
output is the last RSSI indicator to become
active high as the signal strength increases.
See Section 2.2 for details.
RTS
27
RS-232 Request to Send. Active low (TTL
level) input.
RxD
22
RS-232 Receive Data. TTL level output.
RX/SYNC
33
Active high output indicates receive and
synchronization status. See Section 2.2.
TxD
23
RS-232 Transmit Data. TTL level input.
TXMODE
32
Active high output indicates module is
transmitting data over the RF channel. See
Section 2.2.
MHX-920E Operating Manual: Chapter 2 Electrical/Physical
2.2 LED OPERATION
LED functionality is dependent on the mode of operation. Lines RX/SYNC,
TXMODE, and RSSI1,2 and 3 are designed to drive LED’s (active high).
Table 2 explains LED operation for the various modes.
Table 2. LED Operation
LED
MODE
RX/Sync
TXMode
RSSI1,2,3
Power Up (S0=1, S119=1)
off
off
blink 500ms
on/500ms off
Power Up (S0=1, S119=0)
off
off
off
Power Up (S0=0)
off
off
off
Command Mode
off
off
off
on while receiving
valid data packets
from slaves and
repeaters in the
network
on for the first
portion of each
hop interval.
RSSI mode
based on all
received packets
off
off
alternating
300ms on
on for first portion
of hop interval
on for second
portion of hop
interval
RSSI mode
based on packets
received from
Slaves*
Data Mode - Master
Data Mode - Repeater
During Sync. Acquisition
Data Mode - Repeater
When Synchronized
See Table 3
See Table 3
Data Mode - Slave
Sync. Acquisition
Data Mode - Slave
When Synchronized
During
off
off
alternating
300ms on
on
on when
transmitting a
packet.
RSSI mode
based on packets
received from the
Repeater or
Master with
which it
communicates
See Table 3
*If Slaves have been silent for 2 seconds, repeater will base its RSSI on
packets received from the Master.
MHX-920E Operating Manual: Chapter 2 Electrical/Physical
Signal strength, which is also reported in Register S123, is calculated based
on the last four valid received packets with correct CRC, and represented by
RSSI1, 2 and 3.
For slaves, packets are received on every single hop either from a repeater, or
the master.
When calculating RSSI, the master takes into consideration all packets
received from slaves and repeaters. Repeaters and slaves only transmit back
to the master when they have information to send. Therefore, if no data is
coming back to the master then RSSI will never get updated at the master,
and the LED’s will be off.
Table 3 - RSSI mode operation
Signal Strength
(dBm)
RSSI1
RSSI2
RSSI3
-108
50% duty cycle
off
off
-101
on solid
off
off
-93
on solid
50% duty cycle
off
-86
on solid
on solid
off
-79
on solid
on solid
50% duty cycle
-71
on solid
on solid
on solid
MHX-920E Operating Manual: Chapter 2 Electrical/Physical
2.3 DC Characteristics
Sym
Characteristic
Min
Typ
Max
Units
AVCC
Radio Supply Voltage
4.9
5.0
5.5
DVCC
Logic Supply Voltage
4.75
5.0
5.5
VPOT
Power On Reset Threshold Voltage
1.8
2.2
VRST
Reset Pin Threshold Voltage
AICCR
Radio Supply Current in Receive Mode
96
107
117
mA
AICCT
Radio Supply Current at 1mW Transmit
68
108
119
mA
Radio Supply Current at 10mW Transmit
111
123
135
mA
Radio Supply Current at 100mW Transmit
157
174
191
mA
Radio Supply Current at 1W Transmit
398
442
486
mA
DICC
Logic Supply Current
95
105
115
mA
VIL
Input Low Voltage (Pins 23,24,27)
-0.5
.3DVCC
VIH
Input High Voltage (Pins 23,24,27)
0.6VCC
VCC+.5
VOL
Output Low Voltage (Pins 21,22,26,2833)
0.6
VOH
Output High Voltage (Pins 21,22,26,2833)
ISRCE
Sourcing Current (Pins 21,22,26,28-33)
DVCC/
IMPORTANT:
For best performance, it is
strongly recommended to use
a separate, linearly regulated
supply for Vcc Radio. Do
not directly feed a switching
power supply into Vcc
Radio.
For OEM design simplicity,
connect both the radio and
logic Vcc connections
together.
AICCT
AICCT
AICCT
4.2
10
mA
Caution: Using any other power
supply which does not provide the
proper voltage or current could
damage the MHX-920E module.
MHX-920E Operating Manual: Chapter 2 Electrical/Physical
2.4 AC Characteristics
Sym
Characteristic
Min
TTOUT
Reset Delay Time-Out Period
TR2D
Internal Reset to Data Mode*
TR2C
Internal Reset to Command Mode
Typ
Max
500
ms
Units
ms
*Unit will enter into Command Mode upon power up if register S0=0. Unit will enter into Data
Mode upon power-up if register S0=1. When powering up into Data Mode, an additional delay
of 5 seconds is added if Register S119=1. See page 14 for details.
Figure 3 provides timing information for both power-up reset and the \Reset
line operation. A fixed internal reset delay timer of roughly 500ms is
triggered as the VPOT or VRST threshold is reached.
DVCC
VPOT
\Reset
VRST
Internal Reset
Data Mode
(Valid when S0=1)
Command Mode
(Valid when S0=0)
TTOUT
T R2D
T R2C
Figure 3. Reset Timing
MHX-920E Operating Manual: Chapter 2 Electrical/Physical
10
MHX-920E Operating Manual: Chapter 3 Modes of Operation
3. Modes of Operation
The MHX-920E modem can be easily configured to meet a wide range of
needs and applications. The module is designed such that all communication
is through one serial port (Pins 21 to 28 on the module). This port has two
functions:
1.
It provides the asynchronous interface with the host equipment for data
that is sent/received on the RF channel. When operating in this fashion,
the module is said to be in data mode.
2.
It is also used for configuring and programming the module. When
operating in this fashion, the module is said to be in command mode.
In addition to data mode and command mode, there is a third mode of
operation called diagnostics mode. The module will always be in one of
these three modes.
3.1 Data Mode
Data mode is the normal operating mode of the MHX-920E. When in data
mode, the MHX-920E is communicating with other MHX-920E modules,
and facilitating wireless asynchronous serial communication amongst two or
more terminal devices. There are three basic elements to any MHX-920E
communications network:
•
One module configured as the Master
•
Zero or more modules configured as Repeaters
•
One or more modules configured as Slaves
The function of the Master is to provide synchronization for the entire
network, and to control the flow of data. There is always one Master per
network. The Master is the ultimate destination for all data collected at the
various Repeater’s and Slave’s serial ports. With the network set up for
Point-to-Multipoint communication, all data received at the Master’s serial
port is transmitted to every Repeater and Slave in the network. The MHX920E is a frequency hopping transceiver, meaning that it “hops” to a new
frequency after a predetermined time interval. This time interval is a fixed
time set by the user, and can range from 8ms to 120ms. The MHX-920E
hops according to a pseudorandom pattern of 50 different channels.
When configured as a Slave, the MHX-920E searches for synchronization
with a Master. Network topologies consisting of a single Master and
virtually any combination of Slaves and Repeaters may be deployed. The
functionality of any particular MHX-920E can be configured as follows:
MHX-920E Operating Manual: Chapter 3 Modes of Operation
11
n Master Point-to-Point: The modem is configured to
communicate with a single Slave, either directly, or through one
or more Repeaters.
n Master Point-to-Multipoint: The modem is configured to
communicate with one or more Slaves and/or Repeaters.
n Slave: The modem is configured to communicate with one
Master either directly or through one or more Repeaters..
n Repeater: The modem is configured to pass information from
either a Master or another Repeater onto subsequent Repeaters
and/or Slaves and vice versa. The Repeater also acts as a Slave
in the sense that, like a Slave, it passes information to/from its
serial port.
Examples of different network topologies are shown in Figure 4. Network 1
shows Point-to-Point communication between a Master and Slave. Network
2 makes use of a Repeater to communicate with the Slave. Network 3
illustrates a simple Point-to-Multipoint network with no Repeaters. Networks
4 and 5 gives examples of Point-to-Multipoint networks consisting of both
Repeaters and Slaves. There is effectively no restriction to the number of
Repeaters and Slaves that can be added to a network. As seen in Network 4,
a Master can communicate directly with both Slaves and Repeaters.
Network 1
Network 2
3.2 Command Mode
Network 3
The MHX-920E firmware has been designed to allow the user to customize
the operation of the modem through an AT Command Interface. This
interface is ideal for direct interface with another microcontroller or for
higher level Windows-based software applications, but also contains userfriendly built-in register descriptions. These descriptions make it easy for the
user to configure the unit by manually inputting AT Commands and
modifying S-Register parameters, using any standard terminal program. The
MHX-series development board is a useful tool for familiarizing yourself
with the various operating parameters and user interface. Reference
schematics for the development board can be found in Appendix G. To
access the MHX-920E’s command mode using the development board:
Network 4
Network 5
Figure 4 - Sample Network
Topologies. Virtually any
Combination of Slaves and
Repeaters May be Used.
12
1.
Insert the module into the socket with the antenna connector towards the
edge of the board.
2.
Attach the supplied antenna.
3.
Connect a straight through serial cable between the DB9 connector and
the serial port on your PC
4.
Run any terminal application program such as Hyperterminal
5.
Set the serial port to 9600 baud, 8N1
6.
Apply power to the development board
7.
While the three RSSI LED’s are blinking, type ‘mhx’ (you have about 5
seconds to do this). The modem should respond with ‘OK’.
8.
Type ‘AT&V ’
MHX-920E Operating Manual: Chapter 3 Modes of Operation
3.2.1 AT Command Interface
At this point you should see a menu similar to the following appear:
BAUD = 9600
E1 Q0 V1 W0
DCD &C1
DTR &D0
Framing &E0
Handshaking &K3
DSR &S1
S0=1 S2=43 S3=13 S4=10 S5=8
Operating Mode
S101=1
Serial Baud Rate
S102=7
Wireless Link Rate
S103=2
Network Address
S104=1
Unit Address
S105=1
Hop Pattern
S106=0
Encryption Key
S107=1
Output Power
S108=2
Hop Interval
S109=4
Data Format
S110=1
Packet Min Size
S111=1
Packet Max Size
S112=43
Packet Retransmissions
S113=1
Quick enter to command
S119=1
Packet Repeat Interval
S115=1
Character Timeout, ms
S116=8
RTS/DCD Framing, ms
S120=0
DCD Timeout, ms
S121=0
Secondary Hop Pattern
S206=2
Packet Retry Limit
S213=2
Average RSSI value
S123= -0 dBm
Modbus Mode
S117=0
Roaming
S118=0
Packet Size Control
S114=0
Remote Control
S122=0
OK
The MHX-920E is controlled through an AT Command line interface using a
command set which is very similar to a traditional Hayes telephone modem
command set.
All line entries must be preceded by the characters ‘AT’. The characters
‘AT’ are known as the attention characters and must be typed at the
beginning of each command line. For example, to change the operating
mode, type:
ATS101=2 
The modem should respond with ’OK.’ The above command will set the
operating mode to Master Point-to-Point.
Register settings are not immediately stored to non-volatile memory,
therefore if the modem is powered down at this point, the Operating Mode
would revert to its previous value. To store any recently updated command
registers, the following “write” command must be entered.
AT&W 
3.3 Switching Between Command and Data Modes
Your modem must be in command mode for it to execute a command. If
you send characters when the modem is in data mode, the modem transmits
the characters over the air.
Depending on its settings, the modem will either power up in command mode
or data mode. Normally, when first received from the factory, the unit will
power up into data mode. During the first five seconds after power-up, the
user is given the opportunity to avoid entering into data mode but instead
enter into command mode by typing ‘mhx’.
MHX-920E Operating Manual: Chapter 3 Modes of Operation
13
DATA
MODE
(ATA
or A
TO
Com
man
d)
Esc DT
ape R o
Seq r
uen
ce
5 sec elapses
or
characters
other than
'mhx'
entered by
the user
COMMAND
MODE
USER TYPES 'mhx'
POWER-UP
SEQUENCE
Figure 5A. S0=1, S119=1
(factory default)
(AT
Ao
rA
TO
Com
man
d)
Es DT
cap R
e S or
equ
enc
Issuing the answer command (ATA ); or,
•
Issuing the online command (ATO ).
To return to Command Mode, you can either:
Figure 5B. S0=1, S119=0
•
Send the escape sequence. (The escape sequence consists of 1 second of
inactivity, followed by the characters ‘+++’ followed by another second
of inactivity.); or,
•
Toggle the DTR line (depending on the &D parameter see pg 11).
500 msec
(ATA
or A
TO
Com
man
d)
Esc DT
ape R o
Seq r
uen
ce
DATA
MODE
Figure 5C. S0=0
•
The modem will now attempt to communicate with other MHX-920E
modules. While in Data Mode, the modem will communicate through the
serial port at the same baud rate as was last used in Command Mode2.
POWER-UP
SEQUENCE
COMMAND
MODE
In command mode, the module “autobauds,” meaning that it will adapt to the
baud rate of the DTE equipment to which it is connected. Therefore, when in
command mode, you may change the baud rate of your equipment, and the
MHX-920E will automatically adjust to this baud rate once an AT string is
issued. The new baud rate is stored in register S102. Several baud rates
ranging from 2400 to 115200 may be selected.
You can place the modem into Data Mode from Command Mode either by:
DATA
MODE
COMMAND
MODE
The terminal must be set for 9600 baud 8N1 in order for the modem to accept
these characters. If ‘mhx’ is typed incorrectly, the modem will immediately
enter into data mode. If the five seconds elapses without any response from
the user, the modem will go into data mode.
POWER-UP
SEQUENCE
The escape sequence must be issued at the baud rate that the modem has been
set to. If the modem is set to 19200 baud, and the escape sequence is issued
at 9600 baud, for example, the modem will not recognize it, and will not go
into Command Mode.
Figure 5 provides a state diagram for power-up, command mode, and data
mode. Note that there are three different variants of the state diagram which
depend on the values of registers S0 and S119. See the appropriate sections
for more details about these registers. The factory defaults are S0=1 and
S119=1.
500 msec
The escape sequence will not
be accepted unless both the
MHX-920E and the terminal
are set to the same baud rate
14
It is possible to enter into Data Mode at a different baud rate from what is
currently being used in Command Mode by issuing the command ATS102=x,
where x is one of the valid baud rates. Care must be taken when setting the
baud rate in this manner. If you issue another AT string after attempting to
set the baud rate using ATS102 , the modem will again autobaud
and automatically revert to the baud rate of the host equipment. For example,
if your equipment is running at 9600 baud and you wish to set up the modem
to run at 19200 baud, the following command line entry would be suitable:
ATS102=5&WA 
The first part (S102=5) sets the baud rate to 19200. The next characters
(&W) write this baud rate to memory. The last character (A) puts the modem
into Data Mode. Once in Data Mode, the modem is unable to autobaud, and
is fixed at 19200 baud. By combining several commands into one command
line entry, and then immediately putting the modem online, the modem is not
given a chance to autobaud back to 9600.
MHX-920E Operating Manual: Chapter 3 Modes of Operation
4. Configuration
This chapter provides a detailed description of the various operating
parameters of the MHX-920E. Section 4.1 provides a quick-start approach
which outlines the minimum requirements for establishing communication
between two MHX-920E modules. The settings will not necessarily provide
optimal performance for your application, but will verify that the modules are
functioning correctly.
Section 4.2 describes the AT Command interface, and the various AT
Commands. Section 4.3 covers all S-Register parameters which affect the
operation of the modem, and Section 4.4 provides a description of all
diagnostic features of the modem.
4.1 Quick Start Approach
There are several parameters that must be set in order to establish
communication between a pair of MHX-920E modules.
Warning: After testing the units
for correct operation using the
quick-start approach, be sure to
modify some of the security
parameters such as Network
Address and Encryption Key, to
avoid unintentional
communication with other users of
MHX-920E products..
The MHX-920E is equipped with four standard factory default settings.
Instead of manually configuring each individual operating parameter, a global
command may be used to quickly configure the modem for a particular type
of operation. For example, to quickly implement Network 1, Factory default
1 would be applied to the Master, and Factory default 2 would be applied to
the Slave. To quickly set up Network 2, apply Factory 1 to the Master,
Factory 3 to the Repeater, and Factory 4 to the Slave. These defaults will get
you started and only ensure that a link can be established, but do not
necessarily provide the best performance.
Optimization of the
communications link is discussed in later sections.
To implement the basic network illustrated in Figure 6, Network 1,
1.
Insert the module into the development board socket with the antenna
connector towards the edge of the board.
2.
Attach the supplied antenna.
3.
Connect a straight through serial cable between the DB9 connector and
the serial port on your PC
4.
Run any terminal application program such as Hyperterminal and set the
terminal application’s serial port settings to 9600 baud, 8N1
5.
Apply power to the development board
6.
While the three RSSI LED’s are blinking, type ‘mhx’ (you have about 5
seconds to do this). The modem should respond with ‘OK’.
7.
Configure the unit to Factory Setting 1 by typing AT&F1 . This puts
the unit into Master Point-to-point mode.
8.
Store these settings to memory by typing AT&W .
9.
Put the modem into Data Mode by typing ATA (or ATO) 
Network 1
Network 2
Figure 6. Basic Networks
10. Perform above steps for the second unit, using Factory Setting 2 instead of
Factory Setting 1. This will configure the second unit as a Slave.
MHX-920E Operating Manual: Chapter 4 Configuration
15
The units should now be communicating. Remember, the parameters defined
by Factory Settings 1 and 2 will likely not be the most ideal for your
application, but will quickly allow you to test the units. A complete summary
of the settings defined by all four factory settings can be found in Appendix
C. Factory Default Settings.
Settings are not immediately stored in non-volatile memory, therefore, the
command &W is issued to store the current configuration into non-volatile
memory. Settings are retained even after powering down. All user selectable
parameters for the MHX-920E are described in detail in Sections 4.2 and 4.3:
Checking the Link
To check if the units are communicating, observe the LED indicators on the
development board which houses the Slave unit. If the link is good, up to
three RSSI LEDs on the Slave modem should be active along with the
RX/Sync LED, and if the link is absent (due to a fault at one end or another,
such as misconfiguration), the LED’s will be in either “scanning mode” or
inactive. See Section 2.2 for complete LED operation.
Characters typed at the Master terminal should appear at the Slave’s terminal,
and vice versa. Also, verify that the RX LED blinks as packets of data are
received at the Master modem. As data is sent from Slave to Master, the RX
indicator should blink on as correct packets of data are received. At this
point, the Master’s RSSI LED’s should become active. It is recommended
that if the MHX-920E will be deployed in the field where large distances
separate the units, the modems should be configured and tested in close
proximity (e.g., in the same room) first to ensure a good link can be
established and settings are correct. This will facilitate troubleshooting,
should problems arise.
4.2 AT Commands
Several AT Commands are supported by the MHX-920E. These commands
affect the operation of the modem in command mode and the transition
between data and command modes. More commands and S-Register settings
are discussed in Sections 4.3 and 4.4.
To make the command line more readable, you can insert as many spaces as
desired. The command line holds up to 16 characters, not including the AT
prefix. If you want to send more than one command line, wait for a response
before entering the AT prefix at the start of the next command line.
The escape sequence will not
be accepted unless both the
MHX-920E and the terminal
are set to the same baud rate
To re-execute the previous command, enter A/. The modem will execute the
previous command line.
When in Command Mode, the modem “autobauds”, meaning that it will
automatically adjust to the baud rate of the terminal. You may change the
terminal baud rate while in Command Mode without losing communication
with the modem.
For the AT command protocol, an escape sequence consists of three
consecutive escape codes preceded and followed by at least 1 second of
inactivity. Typically, the ‘+’ character is used as the escape code.
+++
16
preceded and followed by 1 second of inactivity
MHX-920E Operating Manual: Chapter 4 Configuration
Note that the terminal must be
configured to the same baud rate
as the modem in order for the
modem to recognize the escape
sequence. The modem is unable
to “autobaud” while in Data
Mode.
The following is a description of
all available commands.
‘*’
denotes standard factory settings.
All of the following commands
must be preceded by “AT”.
Quiet Mode
Your modem is preset to send responses when it executes commands, and
there after to keep the host informed of its status.
*Q0
Q1
Enable modem responses
Disable modem responses
Result Codes display
Your modem can either display result codes as words or numbers.
V0
*V1
Display Result Codes as numbers
Display Result Codes as words
Answer
The A command puts the modem
into data mode, where the
modem attempts to communicate
with other compatibly configured
modems (Type ATA ).
Command Echo
Your modem is preset to return
(or echo) commands to the host
microprocessor when in
Command Mode.
E0
Echo
*E1
Echo
No Command
Command
Identification
The I command returns various
modem information settings.
I0=
String up to 16
characters stored in nonvolatile memory
I1
Product Code
(MHX-920E)
I2
Issue ROM
Check (OK or ERROR)
I3
Product
Identification (Firmware
Version)
I4
Firmware Date
I5
Firmware
Copyright
I6
Firmware Time
I7
Serial Number
On-line Mode
The O command puts the modem
into data mode. This command
is identical to the A command.
MHX-920E Operating Manual: Chapter 4 Configuration
17
W
Connection Result
This parameter determines the modem response at the transition from Data
Mode to Command Mode
*W0
W1
W2
Refer to Appendix A (page
19) for a summary of the
modem commands
Reports computer (DTE) baud rate as CONNECT xxxx
Reports wireless rate between modems as CARRIER
xxxx.
Reports modem (DCE) baud rate as CONNECT xxxx
Reset and load stored configuration
The Z command resets the modem and loads the stored configuration.
&C
DCD (Data Carrier Detect)
The &C command controls the modem’s DCD output signal to the host
microprocessor. This command determines when the DCD is active.
&C0
*&C1
&C2
&D
DCD is always ON
DCD on when modems are synchronized. DCD is always
on when unit is configured as Master.
DCD used for output data framing and Modbus mode. See
page 33 for details.
DTR (Data Terminal Ready)
The &D command controls what action the modem performs when the DTR
input line is toggled. The DTR input is controlled by the host
microprocessor.
&F1
Master
*&D0
&D1
&D2
&D3
&F2
Slave
&F
&F1
Master
&F3
Repeater
&F4
Slave
DTR line is ignored
Not Supported
DTR disconnects and switches to Command Mode
DTR disconnects and resets modem. Modem will remain
in this state until DTR again goes active.
Load Factory Default Configuration
The &F command resets the modem and loads the default factory
configuration.
&F1
&F2
&F3
&F4
&K
Master Point-to-Multipoint. Designed to communicate
with modems configured as &F2 or &F3.
Slave. Designed to communicate with another modem
configured as &F1.
Repeater. Designed to communicate with modems
configured as &F1 and &F4.
Slave working with factory default Repeater and factory
default Master. Communicates directly with Repeater
configured as &F3.
Handshaking
The &K command controls the handshaking between the modem and host
microprocessor.
&K0
&K2
*&K3
18
Disable handshaking
RTS/CTS input data framing. See page 33 for details.
Enable hardware handshaking (RTS/CTS)
MHX-920E Operating Manual: Chapter 4 Configuration
&S
DSR (Data Set Ready)
The &S command controls the DSR line for the modem, and determines
when it is active
&S0
DSR is always ON
*&S1 DSR is ON in Data Mode, OFF in Command Mode
&S2
DTR/DSR signaling. With &S2, Slaves and repeaters
output the state of the master’s DTR on their local DSR line. Master
outputs the state of a slave’s DTR on its local DSR line only in
point-to-point mode (i.e., DTR is a two-way signal transfer in pointto-point mode, and a one-way signal transfer in point-to-multipoint
mode).
&V
View Configuration
The &V command displays all S registers and their current values.
&E
Framing Error Check
This command enables or disables Framing Error Check. When enabled, the
modem looks for the stop bit. If the stop bit is absent, the byte is thrown out.
When enabled, the modem also does a parity check. Note that the data
format (number of data bits, parity type, and number of stop bits) is defined
by S register 110.
*&E0
&E1
Configuration options are
not stored in non-volatile
memory until the WRITE
command (&W) is executed
&W
Disable Framing Error Check
Enable Framing Error Check
Write Configuration to Memory
The &W command stores the active configuration into the modem’s nonvolatile memory.
Sxxx?
Read S register value
This command causes the modem to display the current setting of S register
xxx.
Sxxx=yyy
Set S register value (see section 4.3 S-Registers)
This command sets the specified S register to a value specified by yyy.
MHX-920E Operating Manual: Chapter 4 Configuration
19
AT Command Result Codes
The MHX-920E module can display the results of a command as either text
strings or numerical data. The following chart shows resulting text string and
corresponding numeric result.
10
12
13
14
15
17
18
33
62
64
20
OK
NO CARRIER
ERROR
CONNECT 2400
CONNECT 3600
CONNECT 4800
CONNECT 7200
CONNECT 9600
CONNECT 14400
CONNECT 19200
CONNECT 28800
CONNECT 38400
CONNECT 57600
CONNECT 115200
CARRIER 45000
CARRIER 20000
MHX-920E Operating Manual: Chapter 4 Configuration
4.3 S Registers
Refer to Appendix A (page
45) for a summary of the
S-Registers.
The S Registers described in this section affect the operating characteristics
of the modem.
S Register 0 - Auto Answer
If this register is set to zero, the modem will power up in command mode. If
this register is set to one, the modem will power up in data mode.
S Registers 2 through 5
cannot be stored to nonvolatile memory.
S Register 2 - Escape Code
This register contains the ASCII value of the escape character.
The default value (decimal 43) is equivalent to the ASCII character ‘+’.
Values greater than 127 disable the escape feature and prevent you from
returning to the Command Mode. This register cannot be stored to nonvolatile memory. If the modem is reset, or powered down, the default value
is restored.
Default is ‘+’ (decimal 43).
S Register 3 - CR Control Code
This register contains the ASCII value of the carriage return character.
This is the character that is used to end the command line and is also the
character that appears after the modem sends a response. This register cannot
be stored to non-volatile memory. If the modem is reset, or powered down,
the default value is restored.
Default is ‘CR’ (decimal 13).
S Register 4 - Linefeed Control Code
Register S4 sets the ASCII value of the linefeed character.
The modem sends the linefeed character after sending a carriage return
character when sending text responses. This register cannot be stored to nonvolatile memory. If the modem is reset, or powered down, the default value
is restored.
Default is ‘LF’ (decimal 10).
S Register 5 - Backspace Control Code
Register S5 sets the ASCII value of the backspace character.
This character is both the character created by entering BACKSPACE and
the character echoed to move the cursor to the left. This register cannot be
stored to non-volatile memory. If the modem is reset, or powered down, the
default value is restored.
Default is ‘BS’ (decimal 8).
MHX-920E Operating Manual: Chapter 4 Configuration
21
S Register 101 - Operating Mode
Only one Master can exist
for each network.
The Operating Mode (register S101) partly defines the “personality” of the
MHX-920E module. Allowable settings for this register are 1 through 5 as
follows:.
•
•
•
•
•
S101=1
S101=2
S101=3
S101=4
S101=5
Master Point to Multipoint
Master Point to Point
Slave
Repeater
Master - Diagnostics (see Section 4.4)
The default for this register depends on which factory default is selected as
shown below:
•
•
•
•
Default for Factory Setting &F1 is 1 (Master Point-to-Multipoint)
Default for Factory Setting &F2 is 3 (Slave)
Default for Factory Setting &F3 is 4 (Repeater)
Default for Factory Setting &F4 is 3 (Slave)
1)Master - Point to Multipoint. In any given network, there
is always only one Master. All other units should be configured as either
Slaves or Repeaters. When defined as a Point-to-Multipoint Master, the
modem broadcasts data to all Slaves and Repeaters in the network, and is
also the ultimate destination for data transmitted by all Slaves and
Repeaters. In addition, the Master defines the following network parameters
to be utilized by all other modems in the network (See the appropriate
sections for a complete description of these parameters):
n Maximum Packet Size (S112)
n Minimum Packet Size (S111)
n Wireless Link Rate (S103)
n Hop Interval (S109)
2)Master - Point to Point. This mode of operation is identical
to Master Point-to-Multipoint, with the exception that the Master only
broadcasts to one particular Slave or Repeater. The modem with which
communication occurs is defined by the Unit Address (S105). For example,
if a Slave has been assigned Unit Address 100, and the Master wishes to
communicate with that Slave, the Master must also be assigned a Unit
Address of 100. If there are Repeaters in the network, they will pass the
packet through to the Slave, and vice versa. Because Repeaters also have
Slave functionality (i.e., a Repeater can be connected to a terminal), the
Master can choose to communicate solely with a Repeater. This would be
accomplished by assigning the same Unit Address to both the Master and
the Repeater.
22
MHX-920E Operating Manual: Chapter 4 Configuration
3)Slave. Up to 65535 Slaves may exist in a network, all of which
communicate with the common Master (either directly or via Repeater(s)).
Slaves cannot directly communicate with other. Slaves only provide
acknowledgement for packets of data sent by the Master when the Master is
in Point-to-Point mode. In multipoint mode, multiple slaves would conflict
with one another if they were all trying to acknowledge the Master at the
same time. The Master does, however, send acknowledgements to all
messages it receives from Slaves. The Master initiates communications by
sending a broadcast message to all Slaves. All Slaves are free to respond in
a “Slotted ALOHA” fashion, meaning that each Slave can choose one of
several windows in which to transmit. If there happens to be two Slaves
attempting to talk at the same time, the Master may not receive the data, and
the Slaves therefore would not get an acknowledgement. At this point, the
Slaves would attempt to get the information through at random time
intervals, thus attempting to avoid any more conflicts. Special parameters
which control the Slave’s response characteristics can be modified with S
Registers S115 and S213.
Network 50
Hop Pattern 2
PHP=1
Master
PHP=1
SHP=2
PHP=2
Slave
Repeater
Hop Pattern 1
Figure 7 - Repeater
Operation
Hop Pattern 3
Repeater Slave
PHP=2 PHP=3
SHP=3
Master
PHP=1
HopPattern 1
Repeater
PHP=1
SHP=2
Slave
PHP=2
Hop Pattern 2
Figure 8 - A Network
Utilizing Three Hopping
Patterns
4) Repeater. A more precise title would be Repeater/Slave, because a
Repeater also has much of the same functionality as a Slave. A terminal can
be connected at the Repeater location and communicate with the Master
terminal. There is no restriction to the number of Repeaters in a network,
allowing for communication over virtually limitless distances. The presence
of one Repeater in a network automatically degrades system throughput by
half. Additional Repeaters, regardless of the quantity, do not diminish
system throughput any further. To understand Repeater operation, consider
the module as belonging to two hopping patterns at the same time: The
Primary Hopping Pattern and the Secondary Hopping Pattern. In Figure 7,
the Master belongs to Hopping Pattern 1, and communicates with the
Repeater on this hopping pattern. The Slave belongs to Hopping Pattern 2,
and communicates with the Repeater on this hopping pattern. The whole
system belongs to Network 50 (i.e., all units must be assigned the same
Network Address (S104), which in this case was selected to be 50. Note
that Slaves and Master only communicate on their respective Primary
Hopping Pattern. Repeaters communicate on the Primary Hopping Pattern
when communicating with the Master (or with another Repeater between
itself and the Master). Repeaters communicate on their Secondary Hopping
Pattern when communicating with Slaves (or with another Repeater between
itself and the Slaves). Figure 8 shows another example.
If the Repeater is not also being used as a Slave (there is no DTE connected
to the serial port), it is recommended that the Repeater’s baud rate be set to
115K, and that handshaking be disabled (&K0). This will help ensure a
smooth flow of data through the network.
If there is no DTE connected
to the Repeater, turn off
handshaking (&K0) and set
the baud rate to 115K.
MHX-920E Operating Manual: Chapter 4 Configuration
23
S Register 102 - Serial Baud Rate
The Serial Baud Rate is the current speed that the modem is using to
communicate with the DTE. In command mode, the module “autobauds,”
meaning that it will adapt to the baud rate of the DTE equipment to which it
is connected. Therefore, when in command mode, you may change the baud
rate of your equipment, and the MHX-920E will automatically adjust to this
baud rate once an AT string is issued. The new baud rate is stored in
register S102. If you issue a command to change the value of S102, the
instant you issue another command, the baud rate will revert back to that of
the DTE equipment. Therefore, it is advisable to operate in Command Mode
at the desired baud rate for Data Mode.
See page 14 for additional information.
The possible values are:
*7
10
11
115200
57600
38400
28800
19200
14400
9600
7200
4800
3600
2400
It is generally advisable to choose the highest rate that your terminal
equipment will handle to maximize performance, unless a limitation on the
available bandwidth is desired. If the DTE is a personal computer, the port
can usually be used reliably at 115200. Issuing the &Fx command (factory
default) does not affect the current setting of S102.
The Master determines the
Wireless Link Rate. This
setting on all other modems
is ignored..
S Register 103 - Wireless Link Rate
The Wireless Link Rate is the speed and optimization method for which
modems will communicate over the RF link. It is only necessary to set this
parameter on the Master unit. Units configured as Repeaters and Slaves will
ignore this setting, and adjust automatically to the rate of the Master.
The allowable settings are:
*2
Fast without Forward Error Correction
Fast with Forward Error Correction
Depending on the application requirements, each mode will provide
different throughput and performance. Appendix E. Performance Tables
give some indication of the performance to be expected in each mode.
In general, Forward Error Correction (FEC) reduces throughput, but in some
environments will actually increase throughput. FEC can reduce the number
of bad data packets, and hence reduce the need to retransmit.
24
MHX-920E Operating Manual: Chapter 4 Configuration
S Register 104 - Network Address
Select a Network Address
and assign it to all units
which will be included in the
network.
Warning: Microhard Systems
strongly recommends changing the
Network Address to a value
different than the factory default
before deploying the network.
The Network Address defines the membership to which individual units can
be a part of. By establishing a network under a common Network Address,
the network can be isolated from any other concurrently operating network.
As well, the Network Address provides a measure of privacy and security.
Only those units which are members of the network will participate in the
communications interchange. Valid values for the Network Address range
from 0 to 65535, inclusive.
To enhance privacy and reliability of communications where multiple
networks may operate concurrently in close proximity, it is suggested that an
atypical value be chosen – perhaps something meaningful yet not easily
selected by chance or coincidence.
Default is 1.
S Register 105 - Unit Address
Use the same Unit Address
on both units for point-topoint mode. In multipoint
mode, set each Slave and
Repeater to a different Unit
Address.
Valid Unit Addresses are 1
to 65535.
In point-to-point operation, the Unit Address on both the Master and Slave
(or Repeater) units must be the same. In a multipoint system, the Unit
Address uniquely identifies each Slave and Repeater from one another.
Each unit in a multipoint system must have a unique Unit Address ranging
from 1 to 65535. Do not use 0 as a Unit Address, and do not use a Unit
Address more than once within the same Network. This is required because
the Master must be able to acknowledge each unit individually, based on the
Unit Address.
S Register 106 - Primary Hopping Pattern
S Register 206 - Secondary Hopping Pattern
Since the MHX-920E is a frequency-hopping modem, the carrier frequency
changes periodically according to one of 64 pseudo-random patterns,
defined by the Primary and Secondary Hopping Patterns. Valid entries for
each are 0 through 63. Patterns 0 through 61 are pre-programmed, with
details provided in Appendix F. Patterns 58 through 63 are user-editable
patterns. See Appendix F for details.
The concept of Primary and Secondary Hopping Patterns was introduced in
the discussion of S Register 101 (Operating Mode).
Using the designations M[a,] Rx[a,b] and Sx[a] where:
- M indicates Master;
- R indicates Repeater;
- S indicates Slave;
- x is the Unit Address;
- a is the primary hopping pattern; and,
- b is the secondary hopping pattern;
MHX-920E Operating Manual: Chapter 4 Configuration
25
the following diagrams illustrate the methodology for deploying simple to
complicated networks:
Master
Slave
Master
Repeater
Master
Repeater1
M[1]
←→
S1[1]
M[1]
←→
R1[1,2]
←→
S2[2]
M[1]
←→
R1[1,2]
←→
R2[2,3]
←→
S3[3]
M[1]
←→
R1[1,2]
←→
R2[2,3]
←→
R3[3,4]
←→
S4[4]
Slave
Repeater2
Slave
It is reasonable to consider a Repeater as being both a Slave and a Master,
alternating between Primary and Secondary Hopping Patterns as the unit
changes channel.
Consider R1 in the illustration below.
When
communicating with the Master, R1 is acting like a Slave on Primary
Hopping Pattern 1. When communicating with R2 and S4, R1 is acting like
a Master on Secondary Hopping Pattern 2. If multiple Repeaters are used,
they should have different Secondary Hopping Patterns:
←→
R1[1,2]
M[1]
Slaves and Masters do not
use Secondary Hopping
Patterns
←→
R2[2,5]
←→
S4[2]
←→
R5[1,3]
←→
R6[3,6]
←→
R8[1,4]
←→
S9[4]
←→
S3[5]
←→
S7[6]
Note that all units have a unique Unit Address.
Remember to assign a
unique Unit Address (1 to
65535) to each unit in the
system
Networks of any complexity can be created by linking multiple Repeaters
and Slaves:
←→
R1[1,2]
←→
M[1]
←→
S2[2]
←→
S3[2]
←→
R5[3,6]
R4[1,3]
←→
←→
S11[1]
←→
S12[1]
R8[3,7]
←→
S6[6]
←→
S7[6]
←→
R9[7,8]
←→
S10[8]
With a limitation of 64 hopping patterns, one might suspect that there is a
limitation to the number of repeaters in a system. However, if the units are
far enough away from one another, hopping patterns may be reused in
different sections of the network, without causing interference.
26
MHX-920E Operating Manual: Chapter 4 Configuration
S Register 107 - Encryption Key
All units within a network
must use the same
encryption key.
The Encryption Key provides a measure of security and privacy of
communications by rendering the transmitted data useless without the
correct key on the receiver. Valid Encryption Keys range from 0 to 65535.
Warning: Microhard Systems
strongly recommends changing the
Encryption Key to a value
different than the factory default
before deploying the network.
Keep in mind that all units within the network must use the same key for
communications to succeed.
S Register 108 - Output Power Level
The Output Power Level determines at what power the MHX-920E
transmits. The MHX-920E’s sensitive receiver can operate with very low
power levels, so it is recommended that the lowest power necessary is used;
using excessive power contributes to unnecessary “RF pollution”.
The allowable settings are:
*2
1 mW
10 mW
100 mW
1000 mW
Ideally, you should test the communications performance between units
starting from a low power level and working upward until the RSSI is
sufficiently high and a reliable link is established. Although the conditions
will vary widely between applications, typical uses for some of the settings
are described below:
Power
Use
1 mW For in-building use, typically provides a link up to 300 feet on the
same floor or up/down a level. Outdoors, distances of 10 km can be
achieved if high-gain (directional) antennas are placed high above
ground level and are in direct line-of-sight.
10 mW 200-500 ft indoors, 8-15 km* outdoors.
100 mW 400-800 ft indoors, 15-25 km* outdoors.
1000 mW Typically provides communications up to a distance of 1000 feet or
(1 W) more in-building on the same floor or up/down a few levels,
depending on building construction (wood, concrete, steel, etc.). In
ideal line-of-sight conditions, up to 30 km* or more can be
achieved. Note that only an antenna with a gain of no more than 6
dBi may be used. Any higher is a violation of FCC rules. See
IMPORTANT warning below.
* These outdoor distances assume antennas are mounted at least 100 ft
above ground level
MHX-920E Operating Manual: Chapter 4 Configuration
27
IMPORTANT:
FCC Regulations allow up to 36 dBi effective radiated power (ERP).
Therefore, the sum of the transmitted power (in dBm), the cabling loss
and the antenna gain cannot exceed 36 dBi.
1 mW = 0 dBm
10 mW = 10 dBm
100 mW = 20 dBm
1000 mW = 30 dBm
For example, when transmitting 1 Watt (30 dBm), the antenna gain
cannot exceed 36 - 30 = 6 dBi. If an antenna with a gain higher than 6
dBi were to be used, the power setting must be adjusted appropriately.
Microhard Systems Inc. limits the MHX-920E’s transmitted power to
100mW for all units purchased with antennas with gain above 6dBi.
The hopping interval is
controlled by the master.
The slave and repeater units
will use the hopping interval
setting from the master.
S Register 109 - Hopping Interval
This option determines the frequency at which the modems change channel.
Note that the Master controls this parameter for the entire network. This
setting is ignored in units configured as Slaves or Repeaters.
The allowable settings are:
*4
Warning: Communication will
fail if the hopping interval is not
set according to the guidelines of
Appendix E.;..
8 msec
12 msec
16 msec
20 msec
30 msec
45 msec
80 msec
120 msec
Some of the shorter hop intervals are incompatible in combination with:
•
repeaters in the system;
•
the value set for link rate (S103); and,
•
larger maximum packet sizes (S112).
See Appendix E for optimal Hopping Interval settings in relation to packet
size and link rate.
28
MHX-920E Operating Manual: Chapter 4 Configuration
S Register 110 - Data Format
This register determines the format of the data on the serial port. Allowable
settings are:
*1
10
11
8 bits, No Parity, 1 Stop
8 bits, No Parity, 2 Stop
8 bits, Even Parity, 1 Stop
8 bits, Odd Parity, 1 Stop
7 bits, No Parity, 1 Stop
7 bits, No Parity, 2 Stop
7 bits, Even Parity, 1 Stop
7 bits, Odd Parity, 1 Stop
7 bits, Even Parity, 2 Stop
7 bits, Odd Parity, 2 Stop
9 bits, No Parity, 1 Stop
S Register 111
S Register 112
S Register 114
S Register 116
Packet Minimum Size
Packet Maximum Size
Packet Size Control
Packet Character Timeout
These settings determine the conditions under which the modem will
transmit accumulated data over the air.
When S114=0, the
Minimum and Maximum
Packet Size is controlled by
the Master , therefore, the
Slave and Repeater units will
use the Minimum and
Maximum Packet Size
setting from the Master.
When S114=1, Slave and
Repeater units will use their
local S111 and S112 settings
for packet size control in
point-to-point mode
S Register 111 - Minimum Size
Valid entries for this register are 1 to 255 bytes, which defines the minimum
number of bytes to receive from the DTE before encapsulating them in a
packet and transmitting over the air.
Note that if register S114=0 at any particular Repeater or Slave, that
Repeater or Slave will ignore its own S111 register and abide by the
Master’s S111 setting. If S114=1 at any particular Repeater or Slave, that
Repeater or Slave will use its own local S111 setting. The default for S111
is 1 byte.
S Register 112 - Maximum Size
This setting has a range of 2 to 255, and defines the maximum number of
bytes from the DTE which should be encapsulated in a packet. This value
should be greater than the minimum packet size, but not smaller than is
necessary for reliable communications. If the wireless link is consistently
good and solid, a maximum size of 255 will yield the best throughput
(depending on the higher level protocols of the connected equipment).
However, if the link is poor (e.g., experiencing excessive interference) and
data is frequently retransmitted, the maximum packet size should be
reduced. This decreases the probability of errors within packets, and
reduces the amount of traffic in the event that retransmissions are required.
Note that if register S114=0 at any particular Repeater or Slave, that
Repeater or Slave will ignore its own S112 register and abide by the
Master’s S112 setting. If S114=1 at any particular Repeater or Slave, that
Repeater or Slave will use its own local S112 setting. The default for S112
is 255 bytes.
MHX-920E Operating Manual: Chapter 4 Configuration
29
S Register 114 - Packet Size Control
This register, when set to 1, allows for Repeater and Slaves’ local S111 and
S112 to override those of the Master when the system is operating in pointto-point mode. This may be useful for controlled asymmetrical data flow.
The master always transmits in the first portion of the hop interval, with
slaves and repeaters responding back to the master on the second portion of
the hop interval. Setting the master’s max packet size smaller than that of
the slave would ensure that the master uses less of the available time within
the hop interval for transmitting data, thereby allocating more time for the
slave.
S Register 116 - Packet Character Timeout
This register has valid entries of 0 to 254 milliseconds. The Packet
Character Timeout timer looks for gaps in the data being received from the
DTE. The timer is only activated after the Minimum Packet Size has been
accumulated in the modem. After which, if the timer detects a gap in the
data exceeding the Packet Character Timeout value, the modem will
transmit the data.
The MHX-920E will accumulate data in its buffers from the DTE until one
of the following requirements is met (whichever occurs first):
•
The Maximum Packet Size (in bytes) has been accumulated;
•
The Minimum Packet Size has been accumulated AND the Packet
Character Timeout interval has elapsed.
The default for the Packet Character Timeout is 8 ms. If set to 0 ms, the
unit will buffer exactly the minimum packet size before transmitting.
S Register 113 - Packet Retransmissions
This register applies to both Master and Repeater operation. It does not
apply to Slave operation. In point-to-multipoint mode, the Master will
retransmit each data packet exactly the number of times defined by the
Packet Retransmissions parameter. In point-to-point mode, the Master will
only retransmit the packet if it does not get an acknowledgement from the
slave with which it is communicating. In this case, the Master will continue
to retransmit until an acknowledgement is received, or the retransmission
limit is reached. When the retransmission limit is reached, the Master
discards the packet. The Master retransmits once at the beginning of each
hopping interval until the limit is reached. This parameter is not necessary
in Slave units since all Slaves receive acknowledgement from the Master,
and needn’t blindly retransmit if it has knowledge that the Master has
received the packet.. As discussed previously, the Repeater effectively
behaves as both a Master and a Slave. When the Repeater is tuned to its
Secondary Hopping Pattern (acting as a Master), the Packet Retransmissions
Parameter comes into play. The Repeater will re-send packets of data on to
Slaves or other Repeaters exactly the number of times defined by the Packet
Retransmissions parameter.
Recipients of the packet will discard any duplicates The valid settings for
this parameter are 0 to 255 retransmissions. The default is 1.
30
MHX-920E Operating Manual: Chapter 4 Configuration
S Register 213 - Packet Retry Limit
Packet Retry Limit is analogous to Packet Retransmissions, but specifically
applies to Slaves and Repeaters. This parameter is not used by the Master.
Because the Slave has the advantage of receiving acknowledgements from
the Master, it is not necessary to blindly retransmit each packet. If the Slave
does not get an acknowledgement on the next hop, it will retransmit its
packet. This will continue until the Packet Retry Limit is reached or an
acknowledgement is received. If the limit is reached, the modem will give
up and discard the data. Valid settings are 0 to 255 retries. The default
value is 2.
The Repeater makes use of this parameter when it is tuned to its Primary
Hopping Pattern and is acting like a Slave.
S Register 115 - Packet Repeat Interval
A parameter that is specific to Slaves and Repeaters is the Packet Repeat
Interval.
The allowable settings are 1 through 255. The default is 1.
This parameter defines a range of random numbers that the Slave will use as
the next slot in which it will attempt to send the packet. For example, if this
register is set to 7, the Slave will choose a number between one and seven as
the next slot in which to transmit. Suppose the random number generator
picks 5, then the Slave will transmit in the fifth time slot. A Slave will
transmit a maximum of once per hopping interval, however, depending on
the duration of the hopping interval and the maximum packet size, more
than one slot per hop is potentially available. The Slave will transmit more
frequently when a Repeat Interval with a smaller range is selected. Choose
1 to have the Slave transmit in the first available slot. Choose higher
intervals for less frequent transmission, or to avoid collisions between many
Slaves in the system.
This register is always disregarded and taken as S115=1 in Point-to-Point
mode.
MHX-920E Operating Manual: Chapter 4 Configuration
31
S Register 117 - Modbus Mode
Modbus Mode allows for the MHX-920E to be fully Modbus compatible.
For Modbus operation, the general requirement is to get the packet of data
to the receiving serial port with no gaps in the data. The MHX-920E
incorporates a “Modbus Mode” which implements a delay at the receiving
modem to ensure that no gaps are introduced. For most applications, the
following settings are suitable for Modbus operation:
1.
Set Modbus Mode parameter S117 = 1
2.
Set the minimum packet size (S111) to 1 byte
3.
Set the character timeout S116 (rounded to the nearest ms) to roughly
2.5 byte lengths. For example, at 9600 baud,
S116 = 1/9600 x 10 x 2.5 x 1000 = 2.6ms
Rounded up, S116 = 3ms
4.
Set parameter S121 = 3 byte lengths. For example, at 19200 baud
S121 = 1/19200 x 10 x 3 x 1000 = 1.56ms.
Rounded up, S121 = 2ms
5.
Set S120 as follows:
Slave Side
S120 = (Hop Interval in ms) x (1 + # of Master retransmissions) x (1 +
# of Repeaters over 1)
eg.
Hop Interval S109=4 (20 ms),
Master Retransmissions S113=1
Number of Repeaters in system = 2; then,
S120 = 20 x (1 + 1) x (1 + 1) = 80 ms
Master Side
S120 = (Hop Interval in ms) x (1 + # of Repeaters over 1)
6.
Try to set the hop interval as short as possible while still ensuring
adequate throughput. It is recommended to set the Hop Interval and
Maximum Packet Size as specified in Appendix E. Performance
Tables. For example, for Master to Slave communication with no FEC,
If a throughput of 60kbps is required, set the Hop Interval S109=3, and
set the Maximum Packet Size S112=110.
The allowable settings for this register are:
*0
32
Disabled
Enabled
MHX-920E Operating Manual: Chapter 4 Configuration
S Register 118 - Roaming
This mode is activated on slaves and repeaters by setting register S118=1.
In this mode, a slave/repeater looks for synchronization with a Master
having the same network address and encryption key, but without regard for
the hopping pattern S106. Once the slave/repeater finds such a master, it
tunes to that master’s hopping pattern. If synchronization is lost, the
slave/repeater will again begin searching for a new master. Using this
algorithm, a mobile unit can ‘roam’ and automatically synchronize with a
new master once it loses communication with the previous one. It is
essential that all Masters with which a roaming slave/repeater will be
communicating with use a hopping pattern from within the same group. See
Appendix F. The allowable settings for this register are:
*0
Disabled
Enabled
S Register 119 - Quick Enter to Command
By setting this register to 1, a delay of 5 seconds is introduced at power-up
before the modem goes into data mode. If, during these 5 seconds, the user
enters ‘mhx’ the modem will instead go into Command Mode, and reply
with ‘OK’. The terminal baud rate must be set to 9600 baud. If an incorrect
character is entered, the modem will immediately go into Data Mode. The
default setting is 1 - Enabled.
S Register 120 - RTS/DCD Framing
S Register 121 - DCD Timeout
The MHX-920E supports two special types of data framing:
•
•
Input (or RTS/CTS) Data Framing; and,
Output (or DCD) Data Framing
Input Data Framing is enabled by configuring the Handshaking Parameter as
&K2. This type of framing makes use of the S120 parameter as illustrated
in Figure 9. Parameter S120 can be set to any value between 0 and 254 ms.
RTS
CTS
TXD
Data going into MHX-910
S120 (ms)
0 to 1 ms
Figure 9 - Input Data Framing
MHX-920E Operating Manual: Chapter 4 Configuration
33
To enable output (DCD) data framing, set the Data Carrier Detect parameter
as &C2. This type of framing uses both S120 and S121 registers as shown
in Figure 10. Valid ranges for each parameter are 0 to 254 ms
DCD
RXD
Data leaving MHX-910
S120 (ms)
S121 (ms)
Figure 10 - Output Data Framing
S Register 122 - Remote Control
This register either disables or enables remote control at a repeater or slave
unit. When disabled, a slave/repeater’s settings may be remotely read by the
master, but may not be remotely modified.
When enabled, the
slave/repeater allows the network master full remote control access. See
Section 4.4.3 for details. The default is 0 - disabled.
S Register 123 - RSSI Reading
This register displays the average signal strength in dBm over the previous
four hop intervals. The value in this register is also reflected in status lines
RSSI1,2 and 3. See Section 2.2 for a description of RSSI, and how it is
derived.
34
MHX-920E Operating Manual: Chapter 4 Configuration
4.4 Diagnostics, Statistics and Remote Control
The MHX-920E provides several commands which are very useful for
troubleshooting and analyzing the performance of the radio system.
4.4.1 Spectrum Analyzer Feature (ATG)
Issuing the command ATG ,causes the MHX-920E to perform a
sweep of the entire operating spectrum, giving a signal strength read-out in
dBm for each channel as shown below:
Noise level, '*'- mean value, '.'- max value
ch 1 -138dBm
ch 2 -139dBm
ch 3 -139dBm
ch 4 -139dBm
ch 5 -139dBm
ch 6 -139dBm
ch 7 -130dBm
ch 8 -116dBm
ch 9 -135dBm
...
ch 127 -135dBm *
Paging -135dBm *
Channel 1 is at frequency 902.4 MHz, with all subsequent channels in 200
kHz increments. This feature also displays average received signal strength
for 12 channels above the 902-928 MHz ISM band. This area of the
spectrum is used by paging networks.
When deploying a network, the spectrum analyzer feature is useful for
determining which parts of the ISM band may be noisy. This knowledge
can be used to select an appropriate hopping pattern, or for creating a
custom hopping pattern which avoids those frequencies.
In addition, the presence of extremely high paging noise (> -25dBm) may
indicate a need to install Microhard’s external cavity filter in line with the
antenna. See Chapter 5 for details.
4.4.2 Statistics (ATP)
The ATP  command provides a list of several statistics as follows:
# of
# of
# of
# of
# of
# of
OK
data packets sent = 0
data packets received = 0
Slave's retries = 0
Slave's packets dropped = 0
Slave's sync errors = 0
CRC errors = 0
The MHX-920E starts the statistics count at zero each time the unit is
powered up, or after the ATP command has been issued. By entering the
ATP command, all statistics are cleared back to zero. The maximum limit
for each statistic is 65535.
MHX-920E Operating Manual: Chapter 4 Configuration
35
4.4.3 Remote Control and Diagnostics (S101=5)
This is a very powerful tool which allows user to remotely configure and
interrogate all units in a multipoint system from the Master unit. Simply by
having knowledge of the unit address of each slave/repeater in the system,
users can set the unit address of the master to match that of the
slave/repeater of interest, set S101=5, go online, and interrogate/modify
virtually all parameters of the remote repeater/slave unit. It should be noted
that when the master goes online, all other units belonging to the network
will synchronize with the master, but only the unit whose unit address
matches the master’s will respond to the master’s diagnostic commands.
In addition, in diagnostics mode, the master can change its unit address ‘onthe-fly,’ avoiding the delays of going into command mode, modifying the
unit address, going back online and re-synchronizing with the entire
network, before interrogating a new slave/repeater. The master’s unit
address can be changed while still maintaining synchronization with the
entire network, allowing for quick and efficient diagnostic sessions with all
remote units. Ensure that register S122=1 on any slave/repeater that you
wish to remotely modify.
Table 4 provides a diagnostics command summary. The first column is a
list of commands that may be issued at the master. The second column is
the corresponding remote register. In general, any command issued without
any additional parameters is a read command. For example, if you type:
0 
The remote slave/repeater will send back the value if its S101 register. On
the Master terminal screen, you would see:
(this is the 0 that you typed, echoed back locally)
(this indicates that the remote’s S101=3)
If you type:
04 
This command would change the remote’s operating mode to S101=4
(repeater). The remote unit should return ‘OK’. Remember, if the remote’s
S122=0 (remote control disabled), the remote will respond with ‘ERROR’.
In Table 4, Column 1, the meanings of the format is as follows:
36
COMMAND
A command without (x) indicates that you may not add any
additional parameters. i.e., you may only read back the value
of the remote’s register. You may not modify that register.
The only exception to this is the WRITE command ‘e’. Type
‘e’ to force the write command (&W) at the remote modem.
COMMAND(x)
Indicates this command may be sent with or without a
parameter. Issuing this command without a parameter reads
the corresponding remote’s register. Issuing this command
with the additional parameter ‘x’ changes the corresponding
remote’s register to ‘x’. Remember, any changes you wish to
retain in the event of a powerdown or reset should be stored to
non-volatile memory by issuing the write command ‘e’.
MHX-920E Operating Manual: Chapter 4 Configuration
Table 4 - Remote Control and Diagnostics
Command
Remote Register Description
0(x)
S101
Operating Mode
1(x)
S102
Baud Rate
2(x)
S108
Output Power
3(x)
S110
Data Format
4(x)
S115
Repeat Interval
5(x)
S116
Character Timeout
6(x)
S120
RTS/DCD Framing
7(x)
S121
DCD Timeout
8(x)
S117
Modbus Mode
9(x)
S213
Retry Limit
test string
Read back 'OK' from remote
a1
test string
a2
test string
a3
test string
b(x)
&E
Read back 'Microhard Systems, Inc.' from
remote
Read back 64 character test string from
remote
Read back 255 character test string from
remote
Framing
c(x)
&C
DCD
d(x)
&K
Handshaking
&W
Write
S123
RSSI
g(x)
S104
Network Address
h(x)
S106
Hopping Pattern
I(x)
S206
Secondary Hopping Pattern
j(x)
S113
Retransmissions
k1
statistics
Read # of data packets sent
k2
statistics
Read # of data packets received
k3
statistics
Read # of Slave's retries
k4
statistics
Read # of Slave's packets dropped
k5
statistics
Read # of Slave's sync errors
k6
statistics
Read # of CRC errors
k255
statistics
Clear statistics
l(x)
S119
Quick Enter to Command Mode
m(x)
S118
Roaming
n(x)
S114
Packet Size Control
o(x)
S111
Min Packet Size
p(x)
S112
Max Packet Size
MHX-920E Operating Manual: Chapter 4 Configuration
37
As mentioned previously in this section, there are some settings that can be
changed to the master’s own registers while in diagnostics mode. The most
useful is the unit address. By changing the master’s unit address to that of
another slave in the network while in diagnostics mode, users can quickly
interrogate/modify many different slave’s settings without the delays
associated with switching between command and data modes. The
commands which apply to the master’s own registers are shown in Table 5.
Table 5 - Master Diagnostics Commands
Command
38
Master Register Description
r(x)
S105
Unit Address
S101
back to normal operating mode
t(x)
S109
Hopping Interval
u(x)
S104
Network Address
v(x)
S106
Hopping Pattern
MHX-920E Operating Manual: Chapter 4 Configuration
5. Installation
The installation, removal
or maintenance of all
antenna components must
be carried out by
qualified and experienced
personnel.
The installation, removal or maintenance of all antenna
components must be carried out by qualified and
experienced personel.
The MHX-920E complies with FCC part 15 at the modular level for
operation in the license-free 902-928 MHz ISM band. This chapter
provides guidelines for installing and deploying equipment which
incorporates the MHX-920E module.
5.1 Estimating the Gain Margin
Successful communication between MHX-920E modules is dependent on
three main factors:
•
System Gain
•
Path Loss
•
Interference
System gain is a calculation in dB describing the performance to be
expected between a transmitter-receiver pair. The number can be calculated
based on knowledge of the equipment being deployed. The following four
factors make up a system gain calculation:
1.
Transmitter power (user selectable 0, 10, 20 or 30 dBm)
2.
Transmitter gain (transmitting antenna gain minus cabling loss between
the transmitting antenna and the MHX-920E module)
3.
Receiver gain (Receiving antenna gain minus cabling loss between the
receiving antenna and the module)
4.
Receiver sensitivity (Specified as -105 dBm on the MHX-920E
module)
In the following illustration, the transmitting antenna has a gain of 6 dB, and
the receiving antenna has a gain of 3 dB. The cable loss between the
module and the antenna is 2 dB on both the transmitting and receiving side.
Cable Loss = 2 dB
Antenna Gain = 6 dB
Cable Loss = 2 dB
Antenna Gain = 3 dB
Transmitter
Receiver
30 dBm
Output Power
Sensitivity =
-105 dBm
The power level has been set to 30 dBm (1W) on the transmitter, and the
receiver sensitivity for the MHX-920E is -105 dBm.
System gain would be calculated to be:
30 - 2 + 6 + 3 - 2 + 105 = 140 dB.
MHX-920E Operating Manual: Chapter 5 Installation
39
Base Height (m)
Mobile
Height
(m)
Distance (km)
When deploying your system, care must be taken to ensure the path loss
(reduction of signal strength from transmitter to receiver in dB) between
equipment does not exceed the system gain (140 dB in the above example).
It is recommended to design for a gain margin of at least 10 dB to ensure
reliable communication. Gain margin is the difference between system gain
and path loss. Referring to the same example, suppose the path loss is 100
dB, the gain margin would be 40 dB, which is more than adequate for
reliable communication.
Path loss is a very complicated calculation which mainly depends on the
terrain profile, and the height of the antennas off the ground.
The following table provides path loss numbers for varying antenna heights
and antenna separation: These numbers are real averages taken from rural
environments. They do not apply to urban, non-line-of-sight environments.
Distance
(km)
Base Height
(m)
Mobile Height
(m)
Path Loss
(dB)
15
2.5
116.5
30
2.5
110.9
15
2.5
124.1
15
117.7
15
10
105
16
15
2.5
135.3
16
15
128.9
16
15
10
116.2
16
30
10
109.6
16
30
122.4
16
30
2.5
128.8
Once the equipment is deployed, you can verify the signal strength by
entering into Command Mode and reading Register S123. This register
provides the average signal strength in dBm. The minimum strength for
communication is roughly -105 dBm.
For consistent reliable
communication, you should try to deploy the equipment such that signal
strength exceeds -95 dBm.
40
MHX-920E Operating Manual: Chapter 5 Installation
5.2 Antennas and Cabling
This section describes the recommended procedure for installing cabling
and antennas for use with the MHX-920E module.
5.2.1 Internal Cabling
The most common method for installing the module is to run a cable from
the module’s MCX connector to a reverse TNC bulkhead connector on the
chassis of the equipment as shown in Figure 11. This cable can be
purchased from Microhard Systems.
Reverse TNC Connector
RG316 Cable
with MCX male
connector
and Reverse TNC
bulkhead
connector
MHX-910
MCX female connector
Figure 11. Suggested Internal Cabling
Cable losses are negligible for the short piece used within the chassis.
Additional losses up to 0.5 dB may be present in the MCX and Reverse
TNC connections.
MHX-920E Operating Manual: Chapter 5 Installation
41
5.2.2 Installing External Cables, Antennas and Lightning
Arrestors
The installation, removal or maintenance of all antenna components must be
carried out by qualified and experienced personnel.
The installation, removal or
maintenance of all antenna
components must be carried out
by qualified and experienced
personnel.
Never work on an antenna system
when there is lightning in the
area.
Direct human contact with the
antenna is potentially unhealthy
when the MHX-920E is
generating RF energy. Always
ensure that the MHX-920E
equipment is powered down
during installation.
Never work on an antenna system when there is lightning in the area.
Direct human contact with the antenna is potentially unhealthy when the
MHX-920E is generating RF energy. Always ensure that the MHX-920E
equipment is powered down during installation.
Surge Arrestors
The most effective protection against lightning is to install two lightning
(surge) arrestors. One at the antenna, and the other at the interface with the
equipment.
The surge arrestor grounding system should be fully
interconnected with the transmission tower and power grounding systems to
form a single, fully integrated ground circuit. Typically, both ports on surge
arrestors are N-female.
Cabling
The following coax cables are recommended:
Cable
Loss (dB/100ft)
LMR 195
10.7
LMR 400
3.9
LMR 600
2.5
Factors to take into consideration when choosing a cable are:
•
price;
•
bend radius limitations (the lower performance cables generally can
bend more sharply)
•
performance requirements; and,
•
distance between the equipment and the antenna.
When installing the cable, always begin fastening at the top near the antenna
connector/surge arrestor. The cable must be supported at the top with a
hose clamp or wrap lock, and at 5 ft intervals down the length of the tower.
Over-tightening the fasteners will dent the cable and reduce performance. If
properly grounded surge arrestors are not installed at both the top and the
bottom of the cable, then the cable should be grounded to the tower at these
locations using a cable grounding kit. If the tower is non-conductive, then a
separate conductor, physically separate from the cable, should be run down
the tower.
42
MHX-920E Operating Manual: Chapter 5 Installation
Antenna
Before choosing an antenna, you should have some knowledge of the path
loss and the topology of the equipment. If the equipment is in a fixed
location and is to communicate with only one other unit also in a fixed
location, then a Yagi antenna is suitable. Choose a Yagi with enough gain
to ensure adequate gain margin. When deploying the Yagi, point the
antenna towards the intended target, ensuring the antenna elements are
perpendicular to the ground.
If the equipment must communicate with multiple or mobile transceivers,
then select an Omni-directional antenna with appropriate gain.
The Effective Radiated Power (ERP) emitted from
the antenna cannot exceed +36 dBm ERP.
To comply with FCC regulations,
.you must limit ERP to 36 dBm or
less.
With the MHX-920E set to full power, ERP is calculated as follows:
ERP = 30 - (Cabling and Connector Losses) + (Antenna Gain) < 36
Use the guidelines in the previous section for calculating cable and
connector losses. If cabling and connector losses are 2 dB, then the
maximum allowable gain of the antenna will be 8 dB.
External Filter
Although the MHX-920E is capable of filtering out RF noise in most
environments, there are circumstances that require external filtering. Paging
towers, and cellular base stations in close proximity to the MHX-920E
antenna can desensitize the receiver. Microhard Systems’ external cavity
filter eliminates this problem. The filter has two N-female ports and should
be connected in line at the interface to the RF equipment.
Weatherproofing
Type N and RTNC connectors are not weatherproof. All connectors should
be taped with rubber splicing tape (weatherproofing tape), and then coated
with a sealant.
MHX-920E Operating Manual: Chapter 5 Installation
43
44
MHX-920E Operating Manual: Chapter 5 Installation
A. Modem Command Summary
The following provides a command summary for the MHX-920E module. Factory settings are denoted with a ‘*’.
AT Commands
Answer
Command Echo
E0 No Echo
* E1 Command Echo
Identification
I0 Custom
I1 Product Code
I2 ROM Checksum test
I3 Firmware Version
I4 Firmware Date
I5 Copyright
I6 Firmware Time
I7 Serial Number
On-line Mode
Quiet Mode
* Q0 Enables Result Codes
Q1 Disables Result Codes
Result Codes Display
V0 Display as Numbers
* V1 Display as Words
Connection Result
* W0 Reports DTE as CONNECT xxxx
W1 DTE) rate as CARRIER xxxx.
W2 Reports DCE as CONNECT xxxx
Reset and load stored configuration
&C
DCD (Data Carrier Detect)
&C0 DCD is always on
* &C1 DCD is on when modems are synchronized
&C2 DCD used for output data framing
&D
DTR (Data Terminal Ready)
&D0 DTR ignored
* &D2 DTR disconnects and switches to command
&D3 DTR disconnects and resets modem
&F
Load Factory Default
&F1 Master
&F2 Slave
&F3 Repeater
&F4 Slave through Repeater
&K
Handshaking
&K0 Disable Handshaking
&K2 RTS/CTS Input Framing
* &K3 Enable Handshaking
&S
DSR (Data Set Ready)
&S0 DSR is always on
* &S1 DSR on in data, off in command mode
&S2 DSR/DTR signaling
&V
View Configuration
&W
Write configuration to memory
Sxx?
Read S register value
Sxx=yy
Set S register value
Result Codes
OK
12
CONNECT 9600
NO CARRIER
13
CONNECT 14400
ERROR
14
CONNECT 19200
CONNECT 2400
15
CONNECT 28800
CONNECT 3600
17
CONNECT 38400
CONNECT 4800
18
CONNECT 57600
10
CONNECT 7200
33
CONNECT 115200
64
CARRIER 20000
62
CARRIER 45000
S Registers
S0
Auto Answer
0 = power up in Command Mode,
*1 = power up in Data Mode
S2
Escape code [0...255] default ‘+’ (43)
S3
CR character [0...255] default  (13)
S4
Line Feed [0...255] default  (10)
S5
Backspace [0...255] default  (8)
S101
Operating Mode
1 - Master Point to Multipoint
2 - Master Point to Point
3 - Slave
4 - Repeater
5 - Master Diagnostics
S102
Serial Baud Rate
1 = 115200, 2 = 57600, 3 = 38400
4 = 28800, 5 = 19200, 6 = 14400
*7 = 9600, 8 = 7200, 9 = 4800,
10 = 3600, 11 = 2400
S103
Wireless Link Rate
*2 = Fast w/o FEC
4 = Fast with FEC
S104
Network Address [0...65535]
S105
Unit Address [1...65535]
S106
Primary Hopping Pattern [0...63]
S206
Secondary Hopping Pattern [0...63]
S107
Encryption Key [0...65535]
S108
Output Power Level
0 = 1 mW, 1 = 10 mW, *2 = 100 mW, 3 = 1000 mW
S109
Hopping Interval
1 = 8 msec, 2 = 12 msec, 3 = 16 msec,
*4 = 20 msec, 5 = 30 msec, 6 = 45 msec,
7 = 80 msec, 8 = 120 msec
S110
Data Format
* 1 = 8N1, 2 = 8N2, 3 = 8E1, 4 = 8O1
5 = 7N1, 6 = 7N2, 7 = 7E1, 8 = 7O1
9 = 7E2, 10 = 7O2, 11 = 9N1
S111
Packet Minimum Size [1...Maximum Size]
S112
Packet Maximum Size [2...255]
S113
Packet Retransmissions [0...255]
S213
Packet Retry Limit [0...255]
S114
Packet Size Control
*0=Disabled, 1=Enabled
S115
Packet Repeat Interval [1..255]
Default = 1
S116
Packet Character Timeout [0...254 ms]
S117
Modbus Mode
*0 = Disabled, 1 = Enabled
S118
Roaming
*0 = Disabled, 1 = Enabled
S119
Quick Enter to Command
0 = Disabled, *1 = Enabled
S120
RTS/DCD Framing Interval [0...254 ms]
S121
DCD Timeout [0...254 ms]
S122
Remote Control
*0 = Disabled, 1 = Enabled
S123
RSSI (dBm)
MHX-920E Operating Manual: Appendix A Modem Command Summary
45
46
MHX-920E Operating Manual: Appendix A Modem Command Summary
B. Serial Interface
The MHX-920E module uses 8 pins on the header connector for
asynchronous serial I/O. The interface conforms to standard RS-232 signals
without level shifting, so direct connection to a host microprocessor is
possible.
The signals in the asynchronous serial interface are described below:
DCD Data Carrier Detect - Output from Modem - When asserted (TTL low),
DCD informs the DTE that a communications link has been established with
another MHX-920E.
Modem
(DCE)


←
←


←

Host
Microprocessor
Signal
(DTE)
DCD
RX
TX
DTR
SG
DSR
RTS
CTS
→ IN
→ IN
 OUT
 OUT
→ IN
→ IN
 OUT
→ IN
Arrows denote the direction that
signals are asserted (e.g., DCD
originates at the DCE and tells the
DTE that a carrier is present).
RX
Receive Data - Output from Modem - Signals transferred from the MHX920E are received by the DTE via RX.
TX
Transmit Data - Input to Modem - Signals are transmitted from the DTE via
TX to the MHX-920E.
DTR Data Terminal Ready - Input to Modem - Asserted (TTL low) by the DTE to
inform the modem that it is alive and ready for communications.
SG
Signal Ground - Provides a ground reference for all signals transmitted by
both DTE and DCE.
DSR
Data Set Ready - Output from Modem - Asserted (TTL low) by the DCE to
inform the DTE that it is alive and ready for communications. DSR is the
modem’s equivalent of the DTR signal.
RTS
Request to Send - Input to Modem - A “handshaking” signal which is
asserted by the DTE (TTL low) when it is ready. When hardware
handshaking is used, the RTS signal indicates to the DCE that the host can
receive data.
CTS
Clear to Send - Output from Modem - A “handshaking” signal which is
asserted by the DCE (TTL low) when it has enabled communications and
transmission from the DTE can commence. When hardware handshaking is
used, the CTS signal indicates to the host that the DCE can receive data.
Notes: It is typical to refer to RX and TX from the perspective of the DTE. This should be
kept in mind when looking at signals relative to the modem (DCE); the modem
transmits data on the RX line, and receives on TX.
“DCE” and “modem” are often synonymous since a modem is typically a DCE device.
“DTE” is, in most applications, a device such as a host microprocessor.
MHX-920E Operating Manual: Appendix B Serial Interface
47
48
MHX-920E Operating Manual: Appendix B Serial Interface
C. Sample Schematic Diagram
The following is a sample microprocessor implementation with a MICROCHIP PIC 16C74 and the MHX-920E. The MHX920E performs no level shifting on the serial port, so direct connection to the host microprocessor is possible.
DO NOT CONNECT THE MHX-920E TO RS 232 DRIVER OUTPUTS. DAMAGE TO THE UNIT MAY RESULT.
On this implementation, the onboard SCI of the PIC 16C74 is directly connected pins 2 and 3 of the MHX-920E. The bidirectional Port D is used for asserting or monitoring control signals from the MHX-920E.
The RESET signal is a momentary active low signal asserted by the host microprocessor.
RESET initializes the MHX-920E and places the system in a known state. This signal should be set high after the host
microprocessor has been reset.
PIC16C74
MHX-920
RC7
RC6
RXD
TXD
RD0
RD1
RD2
RD3
RD4
DCD
DTR
DSR
RTS
CTS
RD5
RD6
RESET
31
Power Connections not shown
MHX-920E Operating Manual: Appendix C Sample Schematic Diagram
49
50
MHX-920E Operating Manual: Appendix C Sample Schematic Diagram
D. Factory Default Settings
AT&F1 - Master Default Settings
AT&F3 - Repeater Default Settings
E1, Q0, V1, W0, S0=1, S2=43, S3=13, S4=10, S5=8
E1, Q0, V1, W0, S0=1, S2=43, S3=13, S4=10, S5=8
DCD
DTR
Framing
Handshaking
DSR
Operating Mode
Serial Baud Rate
Wireless Link Rate
Network Address
Unit Address
Primary Hop Pattern
Encryption Key
Output Power
Hop Interval
Data Format
Packet Minimum Size
Packet Maximum Size
Packet Retransmissions
Packet Size Control
Packet Repeat Interval
Character Timeout (ms)
Modbus Mode
Roaming
Quick Enter to Command
RTS/DCD Framing (ms)
DCD Timeout (ms)
Remote Control
Secondary Hop Pattern
Packet Retry Limit
DCD
DTR
Framing
Handshaking
DSR
Operating Mode
Serial Baud Rate
Wireless Link Rate
Network Address
Unit Address
Primary Hop Pattern
Encryption Key
Output Power
Hop Interval
Data Format
Packet Minimum Size
Packet Maximum Size
Packet Retransmissions
Packet Size Control
Packet Repeat Interval
Character Timeout (ms)
Modbus Mode
Roaming
Quick Enter to Command
RTS/DCD Framing (ms)
DCD Timeout (ms)
Remote Control
Secondary Hop Pattern
Packet Retry Limit
&C1 (On)
&D0 (DTR is ignored)
&E0 (Disabled)
&K3 (Enabled)
&S1 (On in Data, Off in Command)
S101=1 (Master P-MP)
S102=7 (9600 baud)
S103=2 (Fast, No FEC)
S104=1
S105=1
S106=0
S107=1
S108=2 (100mW)
S109=4
S110=1 (8N1)
S111=1
S112=43
S113=1
S114=0
S115=1 (Don’t Care)
S116=8
S117=0
S118=0
S119=1
S120=0
S121=0
S122=0
S206=2 (Don’t Care)
S213=2 (Don’t Care)
&C1 (On)
&D0 (DTR is ignored)
&E0 (Disabled)
&K3 (Enabled)
&S1 (On in Data, Off in Command)
S101=4 (Repeater)
S102=7 (9600 baud)
S103=2 (Fast, No FEC) (Set by Master)
S104=1
S105=3
S106=0
S107=1
S108=2 (100mW)
S109=4 (Set by Master)
S110=1 (8N1)
S111=1
S112=43
S113=1
S114=0
S115=1
S116=8
S117=0
S118=0
S119=1
S120=0
S121=0
S122=0
S206=2
S213=2
AT&F2 - Slave Default Settings
AT&F4 -Slave Through Repeater Default Settings
E1, Q0, V1, W0, S0=1, S2=43, S3=13, S4=10, S5=8
E1, Q0, V1, W0, S0=1, S2=43, S3=13, S4=10, S5=8
DCD
DTR
Framing
Handshaking
DSR
Operating Mode
Serial Baud Rate
Wireless Link Rate
Network Address
Unit Address
Primary Hop Pattern
Encryption Key
Output Power
Hop Interval
Data Format
Packet Minimum Size
Packet Maximum Size
Packet Retransmissions
Packet Size Control
Packet Repeat Interval
Character Timeout (ms)
Modbus Mode
Roaming
Quick Enter to Command
RTS/DCD Framing (ms)
DCD Timeout (ms)
Remote Control
Secondary Hop Pattern
Packet Retry Limit
DCD
DTR
Framing
Handshaking
DSR
Operating Mode
Serial Baud Rate
Wireless Link Rate
Network Address
Unit Address
Primary Hop Pattern
Encryption Key
Output Power
Hop Interval
Data Format
Packet Minimum Size
Packet Maximum Size
Packet Retransmissions
Packet Size Control
Packet Repeat Interval
Character Timeout (ms)
Modbus Mode
Roaming
Quick Enter to Command
RTS/DCD Framing (ms)
DCD Timeout (ms)
Remote Control
Secondary Hop Pattern
Packet Retry Limit
&C1 (On)
&D0 (DTR is ignored)
&E0 (Disabled)
&K3 (Enabled)
&S1 (On in Data, Off in Command)
S101=3 (Slave)
S102=7 (9600 baud)
S103=2 (Fast, No FEC) (Set by Master)
S104=1
S105=2
S106=0
S107=1
S108=2 (100mW)
S109=4 (Set by Master)
S110=1 (8N1)
S111=1
S112=43
S113=1 (Don’t Care)
S114=0
S115=1
S116=8
S117=0
S118=0
S119=1
S120=0
S121=0
S122=0
S206=2 (Don’t Care)
S213=2
MHX-920E Operating Manual: Appendix D. Factory Default Settings
&C1 (On)
&D0 (DTR is ignored)
&E0 (Disabled)
&K3 (Enabled)
&S1 (On in Data, Off in Command)
S101=3 (Slave)
S102=7 (9600 baud)
S103=2 (Fast, No FEC) (Set by Master)
S104=1
S105=4
S106=2
S107=1
S108=2 (100mW)
S109=4 (Set by Master)
S110=1 (8N1)
S111=1
S112=43
S113=1 (Don’t Care)
S114=0
S115=1
S116=8
S117=0
S118=0
S119=1
S120=0
S121=0
S122=0
S206=2 (Don’t Care)
S213=2
51
52
MHX-920E Operating Manual: Appendix D Factory Default Settings
E. Performance Tables
The scope of this appendix is to find the best possible performance and maximum packet size at different modes of
operation. The setup assumes a baud rate of 115k, no retries and no retransmissions.
WARNING: Communication will fail if the maximum packet size (S112) exceeds the recommended optimal
packet size. .
Slave <--> Master
Communication.
(No Repeater)
Link Rate
S103=2
Slave <--> Master
Communication.
(No Repeater)
Link Rate
S103=4
Repeater <-->
Master Direct
Communication.
Link Rate
S103=2
Repeater <-->
Master Direct
Communication.
Link Rate
S103=4
Slave <--> Master
Through One or
More Repeaters.
Link Rate
S103=2
Slave <--> Master
Through One or
More Repeaters.
Link Rate
S103=4
Hop
Interval
1 (8 ms)
2 (12 ms)
3 (16 ms)
4 (20 ms)
5 (30 ms)
6 (45 ms)
7 (80 ms)
8 (120 ms)
1 (8 ms)
2 (12 ms)
3 (16 ms)
4 (20 ms)
5 (30 ms)
6 (45 ms)
7 (80 ms)
8 (120 ms)
1 (8 ms)
2 (12 ms)
3 (16 ms)
4 (20 ms)
5 (30 ms)
6 (45 ms)
7 (80 ms)
8 (120 ms)
1 (8 ms)
2 (12 ms)
3 (16 ms)
4 (20 ms)
5 (30 ms)
6 (45 ms)
7 (80 ms)
8 (120 ms)
1 (8 ms)
2 (12 ms)
3 (16 ms)
4 (20 ms)
5 (30 ms)
6 (45 ms)
7 (80 ms)
8 (120 ms)
1 (8 ms)
2 (12 ms)
3 (16 ms)
4 (20 ms)
5 (30 ms)
6 (45 ms)
7 (80 ms)
8 (120 ms)
Optimal Packet
Size (bytes)
14
66
110
154
255
255
255
255
34
54
76
130
210
255
255
N/A
22
44
101
178
255
255
N/A
N/A
16
43
80
174
255
N/A
22
43
93
174
255
255
N/A
N/A
N/A
14
40
80
174
255
Throughput
(kbps)*
20
52
66
74
83
56
31
21
22
28
32
38
43
30
20
N/A
13
21
32
39
31
21
N/A
N/A
12
16
20
20
N/A
13
21
31
38
31
21
N/A
N/A
N/A
12
16
19
20
MHX-920E Operating Manual: Appendix E. Performance Tables
53
54
MHX-920E Operating Manual: Appendix E. Performance Tables
F. Hopping Patterns
This Appendix provides a guide for selecting appropriate hopping patterns (S106,S206). There
are 64 hopping patterns: The first 62 come pre-programmed from the factory as per the table
below. There are 31 patterns in Group A and 31 in Group B. When deploying a network, it is
recommended that you use choose hopping patterns all belonging to the same group. Patterns
have been designed to notch out certain segments of the ISM band.
Pattern Number
Spectrum Used
0, 2, 4, 6, 8, 10, 12
902.4 - 927.6 MHz
14, 16, 18, 20
905.2 - 924.8 MHz
Group A
22, 24, 26, 28
908.0 - 927.6 MHz
Patterns 0,2,4...60
30, 32, 34, 36
902.4 - 907.2, 913.2 - 927.6 MHz
38, 40, 42, 44
902.4 - 912.4, 918.4 - 927.6 MHz
46, 48, 50, 52
902.4 - 917.4, 923.6 - 927.6 MHz
54, 56, 58, 60
902.4 - 922.0 MHz
1, 3, 5, 7, 9, 11, 13
902.6 - 927.4 MHz
15, 17, 19, 21
905.4 - 925.0 MHz
Group B
23, 25, 27, 29
907.8 - 927.4 MHz
Patterns 1,3,5...61
31, 33, 35, 37
902.6 - 907.4, 913.0 - 927.4 MHz
39, 41, 43, 45
902.6 - 912.6, 918.2 - 927.4 MHz
47, 49, 51, 53
902.6 - 917.8, 923.4 - 927.4 MHz
55, 57, 59, 61
902.6 - 922.2 MHz
Patterns 58 to 63 -may be manually entered or edited by entering AT&H at the Command Line, and following the
prompts. Each pattern must use a channel only once, and must consist of exactly 50 channels. There are 127
channels available ranging from Channel 1 at 902.4 MHz up to Channel 127 at 927.6 MHz.
MHX-920E Operating Manual: Appendix F. Hopping Patterns
55
56
MHX-920E Operating Manual: Appendix F. Hopping Patterns
G. Technical Specifications
Electrical/Physical
Data Interface
Asynchronous Serial Port, TTL Levels
Signals
Sig. Gnd, TX, RX, DCD, DSR, DTR, RTS, CTS
Bandwidth / Data Rate
2,400 - 115,200 bps, uncompressed half-duplex,
Approx. 85 kbps sustained in intelligent asymmetrical full-duplex
transmission mode
Communications Range1
30 kilometres (19 miles)
Power Requirements
5 VDC, 1.0 Amp
Power Consumption
600 mA max, 300 mA typical at 1W transmit; 200 mA receive
Operating Frequency
902-928 MHz
System Gain
135 dB
Sensitivity
-105 dBm
Output Power
1, 10, 100, 1000mW (user-selectable)
Spreading Code
Frequency Hopping
Hopping Patterns
64 pseudo-random, user-selectable
Error Detection
CRC-16 with auto re-transmit
Error Correction
Adjacent Channel Rejection
User-selectable Forward Error Correction (FEC)
> 60 dB
In-band Rejection
> 70 dB
Out-of-band Rejection
> 80 dB
Dimensions (LxWxH)
Encl: 3.5” x 2.1” x 1.” (90 mm x 53 mm x 25 mm)
Weight
75 grams
Operating Environment
Temperature: -40 to +70°C
Humidity: 5 to 95%, non-condensing
Storage Temperature
-40 to 90°C
1. Clear line-of-sight, elevated high-gain antennas.
MHX-920E Operating Manual: Appendix G. Technical Specifications
57
58
MHX-920E Operating Manual: Appendix H. Mechanical Drawings
MHX-920E Operating Manual: Appendix H. Mechanical Drawing
750
21
20
3500
Dimensions in thousandths of an inch.
Shaded areas = keep clear.
600
2100
125
40
Pin 1
100
Top View
200
275
1900
Document Number: D1042-02
Friday, July 14, 2000
Size A
800
Rev.
Sheet 1 of 1
#110, 1144 - 29th Ave. N.E.
Calgary, Alberta, Canada
T2E 7P1
Drawn By: NB
MHX Series Mechanical Drawing
Microhard Systems Inc.
225
170
450
dia. 90
H. Mechanical Drawing
59
60
MHX-920E Operating Manual: Appendix H. Mechanical Drawings
I. Glossary
Terminology Used in the MHX-920E Operating Manual
Asynchronous communications A method of
telecommunications in which units of single bytes
of data are sent separately and at an arbitrary time
(not periodically or referenced to a clock). Bytes
are “padded” with start and stop bits to distinguish
each as a unit for the receiving end, which need
not be synchronized with the sending terminal.
Attenuation
The loss of signal power through
equipment, lines/cables, or other transmission
devices. Measured in decibels (dB).
Bandwidth The information-carrying capacity of a
data transmission medium or device, usually
expressed in bits/second (bps).
Baud
Unit of signaling speed equivalent to the
number of discrete conditions or events per
second. If each signal event represents only one
bit condition, then baud rate equals bits per
second (bps) – this is generally true of the serial
data port, so baud and bps have been used
interchangeably in this manual when referring to
the serial port; this is not always the case during
the DCE-to-DCE communications, where a
number of modulation techniques are used to
increase the bps rate over the baud rate.
Bit
The smallest unit of information in a binary
system, represented by either a 1 or 0.
Abbreviated “b”.
Bits per second (b/s or bps) A measure of data
transmission rate in serial communications. Also
see baud.
Byte A group of bits, generally 8 bits in length. A
byte typically represents a character of data.
Abbreviated “B”.
Characters per second (cps) A measure of data
transmission rate for common exchanges of data.
A character is usually represented by 10 bits: an 8bit byte plus two additional bits for marking the
start and stop. Thus, in most cases (but not
always), cps is related to bits per second (bps) by
a 1:10 ratio.
CRC (Cyclic Redundancy Check) An error-detection
scheme for transmitted data. Performed by using
a polynomial algorithm on data, and appending a
checksum to the end of the packet. At the
MHX-920E Operating Manual: Appendix I. Glossary
receiving end, a similar algorithm is performed
and checked against the transmitted checksum.
Crossover cable (Also known as rollover, null-
modem, or modem-eliminator cable) A cable
which allows direct DTE-to-DTE connection
without intermediate DCEs typically used to
bridge the two communicating devices. Can also
be used to make cabled DCE-to-DCE connections.
The name is derived from “crossing” or “rolling”
several lines, including the TX and RX lines so
that transmitted data from one DTE is received on
the RX pin of the other DTE and vice-versa.
Data Communications Equipment (DCE, also
referred to as Data Circuit-Terminating
Equipment, Data Set) A device which facilitates a
communications connection between Data
Terminal Equipment (DTEs). Often, two or more
compatible DCE devices are used to “bridge”
DTEs which need to exchange data. A DCE
performs signal encoding, decoding, and
conversion of data sent/received by the DTE, and
transmits/receives data with another DCE.
Common example is a modem.
Data Terminal Equipment
(DTE) An enddevice which sends/receives data to/from a DCE,
often providing a user-interface for information
exchange. Common examples are computers,
terminals, and printers.
dBm
Stands for “Decibels referenced to one
milliwatt (1 mW)”. A standard unit of power
level commonly used in RF and communications
(n/10)
work. n dBm is equal to 10
milliwatt, so
0dBm = 1mW, -10dBm = 0.1mW, -20dBm =
0.01mW, etc.
DCE See Data Communications Equipment.
DTE See Data Terminal Equipment.
Flow Control
A method of moderating the
transmission of data so that all devices within the
communications link (DTEs and DCEs) transmit
and receive only as much data as they can handle
at once. This prevents devices from sending data
which cannot be received at the other end due to
conditions such as a full buffer or hardware not in
a ready state. This is ideally handled by hardware
using flow-control and handshaking signals, but
61
can be controlled also by software using X-ON/XOFF (transmitter on/off) commands.
Frequency-hopping
A type of spread spectrum
communication whereby the carrier frequency
used between transmitter and receiver changes
repeatedly in a synchronized fashion according to
a specified algorithm or table. This minimizes
unauthorized
jamming
(interference)
and
interception of telecommunications.
Full-duplex
Where data can be transmitted,
simultaneously
and
independently,
bidirectionally.
Half duplex
Exists when the communications
medium supports bi-directional transmission, but
data can only travel in one direction at the same
time.
Handshaking
A flow-control procedure for
establishing data communications whereby
devices indicate that data is to be sent and await
appropriate signals that allow them to proceed.
Line-of-sight
Condition in which a transmitted
signal can reach its destination by travelling a
straight path, without being absorbed and/or
bounced by objects in its path.
Master The station which controls and/or polls one
or more Slave stations in a point-to-point or pointto-multipoint network. Often functions as a server
or hub for the network.
Non-volatile memory
Memory which retains
information which is written to it.
Null modem cable See Crossover cable.
Point-to-point A simple communications network
in which only two DTEs are participants.
Point-to-multipoint
A communications network
in which a Master DTE communicates with two or
more Slave DTEs.
Repeater A device which automatically amplifies
or restores signals to compensate for distortion
and/or attenuation prior to retransmission. A
repeater is typically used to extend the distance
for which data can be reliably transmitted using a
particular medium or communications device.
many newer devices use a compact 9-pin
connector with only the essential signaling lines
used in asynchronous serial communications.
Lines have two possible states: “high” (on, active,
asserted, carrying +3 to +25 V) or “low” (off,
inactive, disasserted, carrying -3 to -25 V).
RTU
(Remote Terminal Unit) A common term
describing a DTE device which is part of a widearea network. Often a RTU performs data I/O and
transmits the data to a centralized station.
Serial communications
A common mode of
data transmission whereby character bits are sent
sequentially, one at a time, using the same
signaling line.
Contrast with parallel
communications where all bits of a byte are
transmitted at once, usually requiring a signal line
for each bit.
Shielded cable
Interface medium which is
internally shrouded by a protective sheath to
minimize external electromagnetic interference
(“noise”).
Slave A station which is controlled and/or polled by
the Master station for communications. Typically
represents one end of a point-to-point connection,
or one of the terminal nodes in a point-tomultipoint network. Often a RTU is linked by a
Slave DCE.
Spread spectrum
A method of transmitting a
signal over a wider bandwidth (using several
frequencies) than the minimum necessary for the
originally narrowband signal. A number of
techniques are used to achieve spread spectrum
telecommunications, including frequency hopping.
Spread spectrum provides the possibility of
sharing the same band amongst many users while
increasing the tolerance to interference and noise,
and enhancing privacy of communications.
Throughput A measure of the rate of data trans-
mission passing through a data communication
system, often expressed as bits or characters per
second (bps or cps).
RS-232
(Recommended Standard 232; more
accurately, RS-232C or EIA/TIA-232E) Defined
by the EIA, a widely known standard electrical
and physical interface for linking DCEs and DTEs
for serial data communications. Traditionally
specifies a 25-pin D-sub connector, although
62
MHX-920E Operating Manual: Appendix I . Glossary

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