RF DataTech ZRT470 ZRT470 Radio Modem User Manual

RF DataTech ZRT470 Radio Modem

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ZRT Manual Page 1 of 37 Rev. J – 11 September 2008

ZRT SERIES

RADIO MODEMS

SETUP, INSTALLATION

OPERATING MANUAL

ZRT Manual Page 2 of 37 Rev. J – 11 September 2008

ZRT Manual Page 3 of 37 Rev. J – 11 September 2008

CONTENTS

1INTRODUCTION........................................................................................ 4

1.1 PRODUCTS COVERED...........................................................................................................4

1.2 IMPORTANT NOTICES..........................................................................................................4

2 PRODUCT OVERVIEW.............................................................................. 5

2.1 GENERAL ................................................................................................................................5

2.2 TRANSMITTER........................................................................................................................5

2.3 RECEIVER................................................................................................................................5

2.4 MPU CONTROL......................................................................................................................6

2.5 PROGRAMMING & CONFIGURATION...............................................................................6

2.6 SOFT MODEM: ........................................................................................................................6

2.7 MODES OF OPERATION .......................................................................................................6

2.8 HANDSHAKING.....................................................................................................................6

2.9 ADDITIONAL FEATURES......................................................................................................7

3SPECIFICATIONS ....................................................................................... 8

3.1 TECHNICAL SPECIFICATIONS............................................................................................8

3.2 APPROVALS AND LICENSING..........................................................................................10

4PRE-PROGRAMMED CHANNEL PLANS............................................ 12

4.1 UK MPT1411/VNS2111 CHANNELS .................................................................................12

4.2 UK MPT1329 CHANNELS....................................................................................................14

5SETUP & INTERFACING......................................................................... 15

5.1 INTERNAL CONSTRUCTION.............................................................................................15

5.2 INTERFACE PORT PIN CONNECTIONS ...........................................................................15

5.3 12VDC POWER......................................................................................................................17

5.4 ANTENNA PORT..................................................................................................................17

5.5 CHANNEL SWITCHES.........................................................................................................17

5.6 PROGRAMMING ..................................................................................................................17

5.7 RF POWER .............................................................................................................................17

5.8 TIME-OUT-TIMER.................................................................................................................18

5.9 INTERNAL MODEM.............................................................................................................18

5.10 RADIO DATA FORMATS.....................................................................................................19

5.11 FORWARD ERROR CORRECTOR.......................................................................................19

5.12 SQUELCH TAIL (DRIBBLE BITS) ELIMINATION .............................................................19

5.13 SERIAL INTERFACE & HANDSHAKING..........................................................................19

5.14 TRAFFIC PROTOCOL & ROUTING MODES......................................................................21

5.15 TRANSMIT & RECEIVE TIMING.........................................................................................22

5.16 POWER CONSUMPTION.....................................................................................................25

5.17 POWER SAVE MODE ........................................................................................................... 25

5.18 “RSSI” RECEIVE SIGNAL STRENGTH INDICATION.......................................................25

5.19 STATUS LEDS........................................................................................................................ 26

6STORE & FORWARD ............................................................................... 27

6.1 STORE & FORWARD BASED ON CLIENT PROTOCOL. .................................................. 27

6.2 MODBUS................................................................................................................................27

6.3 RFT ROUTING PROTOCOL.................................................................................................29

7 INSTALLATION........................................................................................ 32

7.1 INTRODUCTION ..................................................................................................................32

7.2 POWER SUPPLIES.................................................................................................................32

7.3 EFFECTIVE RADIATED POWER (ERP) .............................................................................. 32

7.4 ANTENNAS, COAX FEEDERS & PERIPHERALS..............................................................33

7.5 MOUNTING & INSTALLATION.........................................................................................35

7.6 FIXING DETAILS...................................................................................................................35

ZRT Manual Page 4 of 37 Rev. J – 11 September 2008

1INTRODUCTION

1.1 PRODUCTS COVERED

This manual covers the ZRT Series of low cost, high performance radio modems designed for

data applications in commercial and industrial systems.

The ZRT is an advanced, simplex/half-duplex, data radio for transmission of serial data.

Versions are available with three different serial port configurations:-

A true RS232 interface full handshaking.

As above but with 5V TTL voltage levels on the interface rather than RS232 levels.

An RS232/RS422/RS485 interface with software selection of required mode. (RTS/CTS

and DSR/DTR Handshaking lines looped back to each other in RS232 mode)

Information is provided to assist with configuration, installation, and operation of the products

in point to point or point to multi-point applications. A separate programming manual covers

the use of the associated WinA4P software for programming and configuration of the radios.

Component level servicing is not covered in this document; if the product fails its first line

testing it should be returned to a service centre.

1.2 IMPORTANT NOTICES

1.2.1 Copyright

All rights to this manual are the sole property of R.F. Technologies Ltd. The copying of the

manual in whole or in part by any method without written permission is strictly prohibited.

1.2.2 Right To Change

In the interest of improvement, R.F. Technologies reserves the right to change the technical

specifications or functions of its product without notice.

1.2.3 Software

R.F. Technologies Ltd software is delivered “as is”. R.F. Technologies Ltd does not grant any

kind of warranty or guarantees on its saleability or it’s suitability for use in specific

applications.

Under no circumstances is R.F. Technologies liable for any damages arising from using the

software.

The copyrights relating to all software is the sole property of R.F. Technologies Ltd.

Any coping, editing, translating or modifying is strictly forbidden without prior written consent

from R.F. Technologies Ltd

1.2.4 Safety Critical Applications

The ZRT has not been designed for, nor is it intended for, use in safety critical or life support

applications. No functional warranty is given if the product is used in such applications.

1.2.5 Use

The ZRT radio modems have been designed to work on various licensed and license-free

frequency bands in use around the world. In the license-free bands, the user must ensure that

the radio modem is used under the terms & conditions applicable to the use of the bands

concerned.

In licensed bands, the user must obtain permission and the necessary licenses from the relevant

authorities.

ZRT Manual Page 5 of 37 Rev. J – 11 September 2008

2PRODUCT OVERVIEW

2.1 GENERAL

The ZRT Series has been designed as a range of high specification, low cost radio modems for

stand alone applications or for integration into OEM products.

Through the use of advanced DSP technology, the design has been optimised for reliability and

low current consumption, making the ZRT suitable for operation on remote sites without mains

power.

Applications include security, command & control, data logging, SCADA, telemetry, remote

switching or any similar applications where serial data needs to be transmitted.

The ZRT is available with three different serial interfaces:-

An RS232 interface with all signalling lines to allow full handshaking if required.

A TTL version of the unit which uses 5V TTL voltage levels on the serial interface

connector rather than RS232 signalling levels, but is otherwise the same.

A version with an RS232/RS422/RS485 interface. Required interface mode is selected

using the configuration software. In RS232 mode, the RTS line is looped back to CTS

and the DSR line is looped back to DSR. RS422/RS485 half-duplex (2-wire) or full

duplex (4-wire) modes are both supported.

The data rate on the serial interface can set to a range of values from 150 baud to 38,400 baud,

while the over-air data rate can be independently set to a range of values between 150 baud and

9,600 baud. If high throughput speeds are not required, the modem can be set to a slower over-

air rate to take advantage of the associated improvement in receiver threshold.

The ZRT is available with two different transmit powers. The low power version meets the

licence-exempt ETS300-220 specification while the higher power 5W version meets the tougher

ETS300-113 and the USA and Canadian specifications.

2.2 TRANSMITTER

The transmitter frequency can be user programmed anywhere within it’s pre-aligned

bandwidth. There are two power versions available, 10mW to 750mW and 100mW to 5W. The

transmit power of any particular hardware version can be set accurately within the relevant

range under software control.

2.3 RECEIVER

The receiver is a very low current double conversion superheterodyne with an active balanced

mixer for very good intermodulation performance. Careful attention to spurious response,

adjacent channel and blocking performance, makes the product ideal for crowded telemetry

channels.

To achieve high performance the programmable bandwidth of the receiver has been limited (for

UHF it is 10MHz, + 5MHz from centre frequency), full details are in the technical specification

section.

Should re-alignment be required, the unit can be returned to our service centre.

ZRT Manual Page 6 of 37 Rev. J – 11 September 2008

2.4 MPU CONTROL

The Microprocessor (MPU) is the heart of the product and at the centre is a 128k flash

microprocessor that controls all the interface circuits to the radio module and external

input/outputs. As well as the control functions, the processor provides DSP functionality that

enables modem operation between 150 and 9,600bps. The processor has 128k of flash memory

from which the code is executed and internal EEPROM for storing programmed parameters.

2.5 PROGRAMMING & CONFIGURATION

The parameters of the ZRT are PC programmable via the serial port. Full details of all the

programmable parameters are covered in the separate programming manual. Details of cables

and adaptors needed for the various interface versions are given in Section 5.6.

2.6 SOFT MODEM:

The ZRT has a “soft modem” which allows over-air transmission at rates between 150bps and

9,600bps using a range of different modulation schemes. The over-air rate can be selected by

the operator to optimise link performance.

2.7 MODES OF OPERATION

2.7.1 Transparent Operation

The ZRT can operate transparently without packetising the data and without adding any other

overheads, thereby maximising data throughput rates. It requires no knowledge of the data it is

transmitting. Data is simply transmitted and received with minimal delay.

2.7.2 Protocol specific modem

The radio recognises a complete frame and only transmits and receives data conforming to that

format. No addressing of radios or routing of data is performed. Protocols such as MODBUS &

DNP3 can be supported in this way.

2.7.3 Routing modem

The radios recognise a protocol specific frame and the address to which the frame is to be sent.

Routing information must be stored in each radio for each destination address that requires the

use of repeaters. Any radio in the system can operate as a repeater. The radio does not perform

any acknowledgement or retries. Any protocol using a fixed address field such as MODBUS

can be supported.

2.8 HANDSHAKING

On the RS232 Full Handshaking and TTL versions, transmission control can either use RTS

control signals or be configured for automatic initiation of transmission on receipt of serial data

at the traffic interface. In either case, the radio provides a CTS output which can optionally be

used for flow control.

On the RS232/RS422/RS485 version, transmission is automatic when transmit data is applied.

The DSR line is internally looped back to DSR and, when configured for RS232 mode, the RTS

line is also looped back to CTS.

In all versions, the radio incorporates a 1,024 byte internal buffer to cope with situations where

the interface data rate is higher than the over-air rate.

ZRT Manual Page 7 of 37 Rev. J – 11 September 2008

2.9 ADDITIONAL FEATURES

The ZRT incorporates the following additional features which enhance the usability of the

product and assist with the operation and maintenance of systems using the product:-

2.9.1 Status LEDs:

The ZRT Radio Modems have a number of front panel LED’s to enable the operator to see at a

glance the status of the product and the serial data port.

2.9.2 Time-out Timer

The transmitter within the ZRT has a user programmable time-out timer which allows the

maximum continuous transmission time to be set in order to prevent channel blocking due to a

fault.

2.9.3 Power-Save Modes

The ZRT has both internally controlled and externally controlled power-save modes to reduce

overall power consumption to extremely low levels for operation on sites without mains power.

2.9.4 Squelch Tail Elimination

As a user programmable option, the ZRT can also operate in a packetisation mode where

framing characters are added at the start and end of the user's message prior to transmission

and stripped off again at the receive end prior to passing the user data to the interface

connector. This can be useful in getting rid of any spurious characters which may otherwise be

generated at the end of messages by squelch noise as the receiver mutes and which can affect

old or non-tolerant protocols.

In a high interference environment, enabling packetisation will often help to block reception of

the interfering signals.

2.9.5 Forward Error Correction

The ZRT allows an optional forward error correction to be switched in when the over-air data

rate is 9,600bps. This will improve error performance, but there is an associated data

throughput overhead of around 30% which therefore reduces the effective transmission rate for

the user data. The forward error corrector is not available at lower data rates as it offers no

significant performance enhancement at these lower rates.

ZRT Manual Page 8 of 37 Rev. J – 11 September 2008

3SPECIFICATIONS

3.1 TECHNICAL SPECIFICATIONS

3.1.1 General

Frequency Range: ZRT169/170 138 - 175MHz

ZRT225 175 - 225MHz

ZRT450/470 406 - 512MHz

ZRT869 863 - 870MHz

(50MHz – 950MHz to special order)

Power Requirements: 12VDC (10V – 15.5DC)

Standby: <75uA

Receiver on & decoding: <70mA

Transmitting: 300mA to 2.1A dependent on Tx power

Number of Channels: 80 sequential or 32 discrete user programmable channels.

Min. Programmable

Channel Step: 6.25kHz or 5kHz

Channel Spacing: 12.5kHz, 20kHz or 25kHz

Operating Temp.

Stability: 2ppm –30 to +60ºC

Construction: Aluminium enclosure.

Size: 75mm W x 130mm L x 30mm H (excluding brackets and connectors)

Mounting: Screws to a flat surface.

Weight: 250g

Connectors: DC Power 2-way Klippon Type

Serial Data 9-way D-Type Female

RF BNC (50 ohm)

LED Indicators: TX, Busy, System, RXD, TXD

3.1.2 Transmitter:

RF Output Power: ZRT 169/450/869 10mW - 750mW

ZRT 170/225/470 50mW - 5Watts

Bandwidth: VHF 10MHz without re-alignment

UHF 12MHz without re-alignment

869 30MHz without re-alignment

Internal Modulation: Programmable for FFSK, 2-Level FSK, GMSK or 4-Level FSK.

Max. Deviation: ± 7.5kHz max

Duty Cycle up to 70%

Adj. Channel Power: >65dB at 12.5kHz

Spurious Emissions: As per ETS300-113

Rise Time: < 9mS

ZRT Manual Page 9 of 37 Rev. J – 11 September 2008

3.1.3 Receiver

Sensitivity: 0.25uV (-119dBm) for 12dB SINAD de-emphasised

0.355uV (-117dBm) for 12dB SINAD flat

Bandwidth: VHF 5MHz without re-alignment

UHF 10MHz without re-alignment

869 20MHz without re-alignment

Spurious Response: ZRT 169/450/869 >65dB

ZRT 170/225/470 >80dB

Blocking: ZRT 169/450/869 >85dBuV

ZRT 170/225/470 >90dBuV

Intermodulation: ZRT 169/450/869 >60dB

ZRT 170/225/470 >70dB

Adjacent Channel: >65dB at 12.5kHz

IF Frequencies: 45MHz and 455kHz

Spurious Emissions: ZRT 169/450/869 <ETS 300-220

ZRT 170/225/470 <ETS 300-113

Mute Response Time: <2msec

3.1.4 Internal Modem

Serial Comms: Asynchronous (or Synchronous with custom software).

Baud rate programmable between 150bps and 38,400bps

Interface: /232Full version :- RS.232 complete with signalling lines

/TTL version:- 5V TTL levels rather than RS.232

/232+485 version:- RS.422/RS.485 (2 or 4 wire) or

RS232 with looped back signalling lines.

Parity: Programmable as Odd, Even or None

NRZI: On or Off

Stop bits: Programmable 1 or 2

Data Bits: Programmable 7 or 8

Signalling Formats: Programmable as V23, Bell202 or MPT1327, up to 1200 baud, coherent

FFSK at 2400 baud, GMSK at 4800 baud, 4 Level FSK at 9600 baud.

Synchronous/Async. Programmable as either up to 1200bps, synchronous above 1200bps

Over-air Baud Rate: 150 – 9600bps within 12.5kHz

Bit Error Rate: 150 - 2400 baud less than 1 x 10-3 at –120dBm

4800 baud less than 1 x 10-3 at –117dBm

9600 baud less than 1 x 10-3 at –115dBm (FEC on)

9600 baud less than 1 x 10-3 at –112dBm (FEC off)

Forward Error Corrector (FEC) is a programmable option at 9600bps.

In the interest of improvement the above specifications are subject to change without notice.

ZRT Manual Page 10 of 37 Rev. J – 11 September 2008

3.2 APPROVALS AND LICENSING

The ZRT has been designed to meet the relevant standards outlined below. Should others be

required, please contact the sales office.

3.2.1 UK Approvals

MPT1411/VNS2111: The 5W version of the ZRT has been tested to MPT1411 and the

replacement VNS2111 for licensed applications with a maximum data

rate of 9600bps within a 12.5 kHz channel. A licence is required and the

permitted output power is normally stated on the licence.

MPT1329: The radios meet the requirements of MPT1329

BS2011: The unit complies with the Vibration specification BS2011.

3.2.2 European Approvals

ETS 300-220 The unit meets the specification for European licensed exempt

communications with a maximum RF power level of 500mW. Please

note the permitted power level may vary from country to country.

ETS 300-113 The 5W version of the unit meets the specification for licensed data

radios

ETS 301-489: The unit meets the required CE specification and carries a CE Mark.

EN60950 The unit meets the relevant requirements of this Safety specification.

3.2.3 European Declaration of Conformance

Hereby, RF DataTech declares that the ZRT Series of Radio Modems is in compliance with the

essential requirements and other relevant provisions of Directive 1999/5/EC.

3.2.4 USA FCC Part 90 & 15 & Canadian RSS119

This equipment has been tested and found to comply with the limits for a Class A digital

device, pursuant to Part 15 of the FCC Rules. These limits are designed to provided reasonable

protection against harmful interference when the equipment is operated in a commercial

environment. This equipment generates, uses, and can radiate radio frequency energy and, if

not installed and used in accordance with the instruction manual, may cause harmful

interference to radio communications. Operation of this equipment in a residential area is likely

to cause harmful interference in which case the user will be required to correct the interference

at his own expense.

WARNING: Changes or modifications not expressly approved by RF DataTech could void

the user’s authority to operate the equipment.

This device complies with Part 15 of the FCC Rules. Operation is subject to the condition that

this device does not cause harmful interference.

ZRT Manual Page 11 of 37 Rev. J – 11 September 2008

RF EXPOSURE

WARNING: To satisfy FCC/IC RF exposure requirements for mobile transmitting devices,

a separation distance must be maintained between the antenna connected to this device and

persons during device operation. To ensure compliance, operations at closer than these

distances are not recommended. The following table show the minimum distance for different

gain antennas:

Antenna Gain Minimum Separation Distance

Unity or Less 0.5m

3dB 0.7m

6dB 1.0m

8dB 1.3m

10dB 1.6m

12dB 2.0m

The antenna used for this transmitter must not be co-located in conjunction with any other

antenna or transmitter

This device has been designed to operate with external antennas having an impedance of 50

ohms.

To reduce potential radio interference to other users, the antenna type and its gain should be so

chosen that the equivalent isotropically radiated power (EIRP) is not more than that required

for successful communication and is not higher than permitted levels.

ZRT Manual Page 12 of 37 Rev. J – 11 September 2008

4PRE-PROGRAMMED

CHANNEL PLANS

Using the PC configuration software, the ZRT can be programmed with a number of user

specified or standard channel plans. Standard plans currently include all UK MPT1411 or

MPT1329 channels. Further standard channel plans may become available in later releases of

the configuration software. A mixture of channels from different channel plans can also be

entered discretely using the software.

The following tables show the channel numbers and associated frequencies for various channel

plans:-

4.1 UK MPT1411/VNS2111 CHANNELS

CHANNEL SCANNER OUTSTATIONS

1457.50625 463.00625

2 457.51875 463.01875

3 457.53125 463.03125

4 457.54375 463.04375

5 457.55625 463.05625

6 457.56875 463.06875

7 457.58125 463.08125

8 457.59375 463.09375

9 457.60625 463.10625

10 457.61875 463.11875

11 457.63125 463.13125

12 457.64375 463.14375

13 457.65625 463.15625

14 457.66875 463.16875

15 457.68125 463.18125

16 457.69375 463.19375

17 457.70625 463.20625

18 457.71875 463.21875

19 457.73125 463.23125

20 457.74375 463.24375

21 457.75625 463.25625

22 457.76875 463.26875

23 457.78125 463.28125

24 457.79375 463.29375

25 457.80625 463.30625

26 457.81875 463.31875

27 457.83125 463.33125

28 457.84375 463.34375

29 457.85625 463.35625

30 457.86875 463.36875

31 457.88125 463.38125

32 457.89375 463.39375

33 457.90625 463.40625

34 457.91875 463.41875

35 457.93125 463.43125

36 457.94375 463.44375

37 457.95625 463.45625

38 457.96875 463.46875

ZRT Manual Page 13 of 37 Rev. J – 11 September 2008

39 457.98125 463.48125

40 457.99375 463.49375

41 458.00625 463.50625

42 458.01875 463.51875

43 458.03125 463.53125

44 458.04375 463.54375

45 458.05625 463.55625

46 458.06875 463.56875

47 458.08125 463.58125

48 458.09375 463.59375

49 458.10625 463.60625

50 458.11875 463.61875

51 458.13125 463.63125

52 458.14375 463.64375

53 458.15625 463.65625

54 458.16875 463.66875

55 458.18125 463.68125

56 458.19375 463.69375

57 458.20625 463.70625

58 458.21875 463.71875

59 458.23125 463.73125

60 458.24375 463.74375

61 458.25625 463.75625

62 458.26875 463.76875

63 458.28125 463.78125

64 458.29375 463.79375

65 458.30625 463.80625

66 458.31875 463.81875

67 458.33125 463.83125

68 458.34375 463.84375

69 458.35625 463.85625

70 458.36875 463.86875

71 458.38125 463.88125

72 458.39375 463.89375

73 458.40625 463.90625

74 458.41875 463.91875

75 458.43125 463.93125

76 458.44375 463.94375

77 458.45625 463.95625

78 458.46875 463.96875

79 458.48125 463.98125

80 458.49375 463.99375

ZRT Manual Page 14 of 37 Rev. J – 11 September 2008

4.2 UK MPT1329 CHANNELS

The ZRT can be programmed to operate on the full MPT1329 band of channels with access to

channels 26, 27 & 32 denied, in line with MPT1329 band plan.

The radio should be programmed for a maximum power level of 500mW.

CHANNEL FREQUENCY

1458.5000 Guard Ch.

2 458.5125

3 458.5250

4 458.5375

5 458.5500

6 458.5625

7 458.5750

8 458.5875

9 458.6000

10 458.6125

11 458.6250

12 458.6375

13 458.6500

14 458.6625

15 458.6750

16 458.6875

17 458.7000

18 458.7125

19 458.7250

20 458.7375

21 458.7500

22 458.7625

23 458.7750

24 458.7875

25 458.8000

26 458.8125

27 458.8250 Not Used

28 458.8375 Not Used

29 458.8500

30 458.8625

31 458.8750

32 458.8875

33 458.9000 Not Used

34 458.9125

35 458.9250

36 458.9375

37 458.9500 Guard Ch.

ZRT Manual Page 15 of 37 Rev. J – 11 September 2008

5SETUP & INTERFACING

5.1 INTERNAL CONSTRUCTION

The exploded view shows the main components of the radio modem. There are no user

adjustments or settings which require removal of the covers.

5.2 INTERFACE PORT PIN CONNECTIONS

The ZRT Series is equipped with a 9 way female D connector for the traffic interface. The pins

of this connector are allocated as follows:-

5.2.1 RS232-Only (Full Handshaking) and 5V TTL versions

1. DCD: Data Carrier Detect - - - o

2. RXD: Receive Data - - - - - - -

o- - - - - 6. DSR: Data Set Ready

o- - - - - 7.

o- - - - - 8.

4. DTR: Data Terminal Ready - - o

o- - - - - 9. nc Not Connected

RTS: Request to Send

TXD: Transmit Data - - - - - - - o

CTS: Clear to Send

GND: GROUND - - - - - - - - - - o

ZRT Manual Page 16 of 37 Rev. J – 11 September 2008

5.2.2 RS232/RS422/RS485 Versions

The RS232/RS422/RS485 versions of the ZRT may be software programmed to have either an

RS232 or an RS422/RS485 compatible interface.

To allow programming without an interface adapter, a radio programmed for RS422/RS485

operation will switch back to RS232 operation if the front panel rotary switches are set to

position 00 to select programming mode. Note that although the ZRT can withstand RS232

voltages on its inputs in RS422/RS485 mode, this may not be the case for externally connected

devices. To avoid any risk of damage to the externally connected equipment, care must

therefore be taken to ensure that programming mode is not selected while connected to

RS422/RS485 terminal equipment.

Pin allocation when set for RS232 operation:-

o- - - - - 9. nc Not Connected

4. DTR: Data Terminal Ready - - - - - - - o

(Internally connected to Pin 6)

o- - - - - 8. CTS: Clear to Send

(Internally connected to Pin 7)

: Transmit Data Input - - - - - - - -TXDo

- - - - - 7. RTS: Request to Sendo (Internally connected to Pin 8)

2. : Receive Data Output - - - - - - - -

RXD o

o- - - - - 6. DSR: Data Set Ready

(Internally connected to Pin 4)

GND: GROUND - - - - - - - - - - - - - - - o

1. Data Carrier Detect - - - - - - - - -

DCD: o

Pin allocation when set for RS422/RS485 operation:-

o- - - - - 9. nc Not Connected

4. DTR: Data Terminal Ready - - - - - - - o

(Internally connected to Pin 6)

o- - - - - 8. *****: Do Not Use

(Internally connected to Pin 7)

: +ve Data In to Radio - - - - - - - -TXD +o

- - - - - 7. : -ve Data In to RadiooTXD -

(Internally connected to Pin 8)

2. : -ve Data Out from radio - - - - - -

RXD - o

o- - - - - 6. DSR: Data Set Ready

(Internally connected to Pin 4)

GND: GROUND - - - - - - - - - - - - - - - o

1. : +ve Data Out from radio - - - - -

RXD + o

When half-duplex (2-wire) RS422/RS485 operation is programmed, the TXD- and TXD+ signals

are internally connected to the RXD- and RXD+ signals respectively. The 2-wire half-duplex

bus only needs to be connected to the RXD- and RXD+ pins (Pins 1 and 2). Shorting links are

not required in the connector.

When operating in 2-wire RS422/RS485 mode, the radio will output data on to a 2 wire circuit

whenever it is received, which could lead to a bus conflict in conditions of high interference and

prevent a connected terminal from outputting transmit data. To avoid this condition it is

recommended that the message packeting option is turned on at both ends of the radio link.

The DTR and DSR signals are looped back to each other internally in both configurations.

When configured for RS232 operation, the RTS and CTS signals are also looped back to each

other. The radio should in most circumstances operate correctly in applications requiring

RTS/CTS handshake although the it is unable to use CTS to prevent buffer overflow. Overflow

situations can easily be avoided by making the serial port baud rate the same as the radio signal

baud rate, or by ensuring that message sizes do not exceed the buffer size of 1024 bytes.

ZRT Manual Page 17 of 37 Rev. J – 11 September 2008

The DTR input has a threshold of approximately +1.5V with respect to ground, it may be used

with a standard RS232 level signal or a TTL level signal in either RS232 or RS485 mode, the

signal is active high in both cases.

5.3 12VDC POWER

A nominal 12VDC (9.6 – 15.5Vdc) is supplied to the unit via a 2 way pluggable terminal block,

the polarity is marked on the front panel and the plug has a polarity key to prevent accidental

polarity reversal. In the event of a polarity reversal the circuit board is protected by diodes and

fuses.

5.4 ANTENNA PORT

The antenna connection is a 50 ohm BNC connector. This should be connected to a suitable

antenna or terminated in a 50 ohm load whenever the transmitter is activated. Transmission

into an open circuit may cause excessive current to be drawn from the supply and damage

could occur.

5.5 CHANNEL SWITCHES

The ZRT can be user programmed with up to 80 sequential or 32 discrete simplex or semi-

duplex channels.

The two front panel BCD switches select the required channels or, if both are set to zero,

program mode is entered. In program mode, the radio interprets any signals on the serial

interface as programming commands rather than data for transmission.

When viewing a ZRT with the aerial connector at the top, the left hand rotary switch is the

"tens" switch and the right is the "units" switch, thus to set channel 37, set the left switch to 3

and the right to 7.

5.6 PROGRAMMING

The parameters of the ZRT can be programmed via the serial port using either DOS or

Windows based software. The individual configuration files can be stored on disc for future

use or printed. Full details of all the programmable parameters are covered in the separate

programming manual.

The RS232 Only (Full Handshaking) version can be connected directly to the serial port on a PC

using a straight-through cable.

The 5V TTL version needs an adaptor unit between the ZRT and the programming computer to

convert between RS232 and TTL voltage levels.

The RS232/RS422/RS485 version does not need an adaptor because the serial port switches to

RS232 mode automatically when the radio is put into program mode by setting both front panel

switches to zero. A standard straight-through cable with all pins connected may be used for

connection to the PC.

5.7 RF POWER

The transmit power can be accurately set using a locally connected PC running the supplied

configuration software. This allows the RF power level to be programmed directly in Watts or

milliwatts with an accuracy of +/-1dB. There are no internal power adjustment points inside

the modem.

There are two transmit power ranges available. The low power ZRT169, ZRT450 & ZRT869

versions can be set between 10mW and 750mW, while the higher power ZRT170, ZRT225 &

ZRT470 versions can be set between 50mW and 5W.

ZRT Manual Page 18 of 37 Rev. J – 11 September 2008

5.8 TIME-OUT-TIMER

The transmitter within the ZRT has a time-out timer which allows the maximum continuous

transmission time to be set in order to prevent channel blocking due to a host fault. The timer

works in all modes (external/internal modem) and is programmable in one second steps

between 0 and 255 seconds. If not required the timer can be programmed off.

If the timer is enabled and the selected time is exceeded, transmission will cease until the action

that normally causes transmission is removed and then re-applied. More explicitly; with

RTC/CTS handshake enabled RTS must be dropped and then raised again, or if handshake is

not enabled character transmission must be suspended for at least two character periods at the

serial port baud rate. In all modes the modem’s SYS led is flashed at least twice when time-out

occurs, the flashing continues while lockout is in force. The lockout timer is disabled if the

lockout time is set to 0. The lockout timer can be operated in “resettable” or “cumulative”

mode, in resettable mode the timer restarts each time a transmission is made, in cumulative

mode the timer counts up during transmit, and down during receive. If the timer counts up to

the lockout time during transmit, lockout occurs; this will eventually happen if the radio spends

more than half of its time transmitting. Lockout in this mode is indefinite and can only be reset

by powering the radio off.

5.9 INTERNAL MODEM

The ZRT features an internal “soft modem” which offers unparalleled performance and

flexibility over a wide range of speeds and formats. Data is presented to the modem via the

RS232 (or TTL) serial connection at speeds between 150 and 38400 and then transmitted at the

programmed radio baud rate. Buffering is provided when the data rate is higher than the radio

transmission rate.

5.9.1 Modulation & Tone-sets

Within a 12.5kHz channel, the over-air transmission from the unit can be programmed for a

range of speeds. For 150, 300, 600,1200, the modulation is FFSK with Bell 202 and V.23 (Mode 2)

tone-sets both supported. At these lower speeds, it is also possible to select a protocol specific

MPT1327 mode which uses a 1200/1800Hz tone-set to allow compatibility with number of

additional modems from other manufacturers. At 2400bps the modulation is coherent FFSK, at

4800bps it is GMSK and at 9600bps it is 4-Level FSK.

If operating at speeds up to and including 1200bps and compatibility with other equipment is

not required, the use of the Bell 202 tone-set is recommended, as this will give the best link

performance.

5.9.2 Synchronous/Asynchronous Modem Operation

The radio modem can be programmed for asynchronous or synchronous operation at baud

rates up to 1200. At baud rates of 2400 or more, modem operation may only be synchronous.

This relates to the over-air signal and has no bearing on the format of the data presented at the

serial interface port

In synchronous mode inverted NRZI encoding is used where a one is represented by a

transition in the binary data, every transmitted bit fits into a time slot defined by the baud rate,

this allows a phase locked loop to lock on to the data stream to give better performance in noisy

conditions, the inverted NRZI encoding allows this to continue even when the signal is idling

sending stop bits. The inverted NRZI encoding gives a further advantage with GMSK signalling

since the polarity of the signal is unimportant.

In asynchronous mode NRZ encoding is used where a “one” tone represents a binary one, and

a “zero” tone a binary zero, whilst each character consists of bits of equal duration defined by

the baud rate, the time between the end of a stop bit and a following start bit may be arbitrary.

This prevents the implementation of a phase locked loop to improve signal to noise

performance but does allow use within older systems that do not implement synchronous

transmission or NRZI encoding.

ZRT Manual Page 19 of 37 Rev. J – 11 September 2008

If compatibility with other radios is not required, the use of the synchronous mode is

recommended, as this will give best link performance.

5.10 RADIO DATA FORMATS

The data rate over the air can be set up independently of the rate set for the serial interface, but

the over-air rate should be set either at the same speed or a lower speed than the serial interface

rate. The radio baud rate should be set at the minimum possible to maintain the required

throughput, lower speeds will give better results in poor signal conditions

The radio signal can be set up to operate using 7 or 8 bit data, 1 or 2 stop bits, and odd, even or

no parity. This setting is also independent of the serial port setup. This flexibility allows

compatibility with other radios.

If the Forward Error Corrector is enabled (option only available at 9,600bps), the selected radio

signal format is over-ridden as detailed below.

5.11 FORWARD ERROR CORRECTOR

At 9600bps there is also a programmable option to switch in a forward error corrector. When

switched on, the over-air data format changes to a fixed format using 14 bit words. These

comprise 8 data bits, 5 CRC (Cyclic Redundancy Check) bits and a flag bit which is used to

differentiate control and data functions in messages. An additional 14 bit synchronisation word

is also sent after every 8 data words. The effect of this redundancy on a typical 9600bps link

configuration is to reduce the effective data transfer rate to around 6300bps.

The error corrector is aimed at improving performance in weak signal conditions, rather than

recovering data in deep fades or burst-error conditions. An error rate of 1x10-4 with the FEC

switched off will typically improve by a factor of 2000 to around 5 in 10-7 when it is switched on,

but an initial error rate of 1x10-3 with it off will only improve by a factor of around 250 to

something like 4x10-5 when it is switched on.

In terms of receiver sensitivity, the 1x10-6 threshold improves by around 0.4uV (or 6.4dB) when

the FEC is switched on.

5.12 SQUELCH TAIL (DRIBBLE BITS) ELIMINATION

The ZRT has an optional packetisation mode which can be enabled using the configuration

program. This adds framing characters at the start and end of the user’s message prior to

transmission. The additional information is stripped off the messages at the receiver prior to

passing the data to the interface connector. Packetisation can be useful in getting rid of any

spurious characters which may otherwise be generated at the end of messages by squelch noise

as the receiver mutes or by interference and which can affect old or non-tolerant protocols.

It is important to note that packetisation must be set the same on all radios operating together.

All radios must have it selected or all radios must have it de-selected.

5.13 SERIAL INTERFACE & HANDSHAKING

5.13.1 Handshaking on RS232/RS422/RS485 version

In this version of the ZRT, transmission is automatic when transmit data is applied.

When configured for RS232 mode, the RTS line is looped back to CTS and the DSR line is

looped back to DSR. The radio should in most circumstances operate correctly in applications

requiring RTS/CTS handshake although the it is unable to use CTS to prevent buffer overflow.

Overflow situations can easily be avoided by making the serial port baud rate the same as the

radio signal baud rate, or by ensuring that message sizes do not exceed the buffer size of 1024

bytes.

ZRT Manual Page 20 of 37 Rev. J – 11 September 2008

5.13.2 Handshaking on RS232-Only (Full Handshaking) and TTL versions

The RS232 Only (Full Handshaking) and TTL versions can be programmed either to use

RTS/CTS handshaking to initiate transmission, or to transmit automatically whenever data is

present at the serial input. In the latter mode CTS is still operated to implement flow control but

can be ignored unless message sizes exceed 1k byte and the serial port baud rate is higher than

the radio signal baud rate. These handshaking modes are compatible with modes A, C and D of

the CMD400 manufactured by Pacscom Ltd.. Mode B (byte stuffing mode) is not supported.

Transmission Using RTS/CTS Handshaking (RS232-Only and TTL Versions):-

If handshaking is enabled, transmission is started by operating RTS. CTS can then be monitored

for flow control purposes. In the idle state CTS is inactive, but when RTS is operated CTS will

become active immediately and data may be input to the serial port. When all data has been

loaded to the serial port RTS should be dropped. Transmission will continue until all data in

the serial input buffer has been sent, then CTS will become inactive and transmission will cease.

During transmission the amount of data in the serial buffer is checked by the radio, if the buffer

becomes ¾ full CTS is dropped to request the host to stop loading data, CTS is activated again

when the buffer is reduced to ¼ full. To prevent timing problems data will still be accepted into

the buffer when CTS is de-activated due to buffer filling during transmit, however any data

received once CTS has dropped at the end of a transmission will be discarded, this prevents

such data from being prefixed to the beginning of the next message.

Transmission Without Hardware Handshaking (RS232-Only and TTL Versions):-

If RTS/CTS handshaking is disabled the radio will start transmission as soon as data is received

at the serial port, transmission ceases as soon as the serial buffer has been emptied and a period

equivalent to two characters at the radio signal baud rate has elapsed. It is important to note

that since transmission ceases as soon as a two character delay in the incoming data stream is

seen, data characters in a message must be presented in a continuous back to back stream.

In this mode CTS is still used to indicate the serial buffer fill level in the same way as described

in the section on transmission using handshake, the difference is that in the idle state CTS is

always active indicating readiness to accept data. In most applications CTS can be ignored as

messages are likely to be smaller than the serial input buffer (1k byte), bear in mind also that if

the radio baud rate and data format is the same as that configured for the serial port the buffer

is being emptied as fast as it is being filled and so buffer overrun is unlikely.

5.13.3 Data Reception

Any data received by the radio is simply output to the serial port, and in RS232 configurations

the DCD line can be programmed to operate in three different modes to assist the host. Firstly

by indicating that a carrier is detected on the radio channel, this is useful if a busy lockout

function is required (although this can be dangerous if the channel is susceptible to interference

as well as wanted signals), secondly DCD can indicate presence of a carrier and a valid data

signal, data will normally be output under this circumstance, the third mode behaves in the

same way as the second except that DCD remains active until all data has been output to the

serial port after the signal has gone, this allows DCD to be used as a wake up signal.

In RS422 and RS485 2-wire configurations, the radio will output data on to the 2 wire circuit

whenever it is received, which could lead to a bus conflict in conditions of high interference,

preventing any connected terminal from transmitting data when it wants to. To avoid this

condition it is recommended that the message packeting option is turned on at both ends of the

radio link in this mode.

ZRT Manual Page 21 of 37 Rev. J – 11 September 2008

5.14 TRAFFIC PROTOCOL & ROUTING MODES

5.14.1 Transparent Mode

In this mode, the radio has no knowledge of the data it is transmitting, data is simply

transmitted and received under hardware control with the option of RTS control or initiation of

transmit after receiving serial data, with CTS providing an optional flow control. This

configuration is useful when expanding older systems where the radios must be compatible

with other manufacturers equipment.

5.14.2 Protocol Specific Mode

The radio recognises a complete frame and only transmits and receives data conforming to that

format. No addressing of radios or routing of data is performed. Protocols such as MODBUS

can be supported in this way.

5.14.3 Routing Mode

The radios recognise a protocol specific frame and the address to which the frame is to be sent.

Routing information must be stored in each radio for each destination address that requires the

use of repeaters or store & forward nodes. Any radio in the system can operate as a

repeater/store & forward node. The radio does not perform any acknowledgement or retries.

Any protocol using a fixed address field such as MODBUS or RFT ROUTING can be supported.

5.14.4 STORE & FORWARD OPERATION

The ZRT can support “Store & Forward” repeater operation to cope with situations where the

direct communication between sites is not possible due to range or terrain. The ZRT series

supports up to six repeaters within one link, although the more repeaters used, the greater the

signal strength has to be at each receiver, as there will be some accumulative degradation over

the whole link.

The forwarding is carried out based on the Protocol Routing Mode and is based on the address

fields within the data to be transmitted. At a repeater site, the incoming message is stored and

then re-transmitted if it is for a protocol address further down that chain of radios.

ZRT Manual Page 22 of 37 Rev. J – 11 September 2008

5.15 TRANSMIT & RECEIVE TIMING

The ZRT only operates in a simplex or semi-duplex mode. In simplex mode the receive and

transmit frequencies are the same, whereas in the semi-duplex mode they are different.

In either mode data is only sent in one direction at a time as the radios do not have separate

synthesisers for transmit and receive. If full duplex mode is required (transmit & receive at the

same time) the ART product should be considered.

In simplex/semi-duplex mode, the radio synthesiser must be reloaded each time Receive or

Transmit is selected. Although relatively short, the synthesiser loading time must be taken into

account when looking at data transfer times.

In order to reduce adjacent channel interference in line with ETS300-113, the power output from

the transmitter has finite rise and fall times, a distant receiving radio will therefore see an

incoming signal later than a nearby one. The receiving radio also requires time for the carrier

detect circuit to operate and for the modem to lock on to the incoming audio signal.

When using the ZRT, there are a few timing considerations to be taken into account. The main

one is the programmable “lead in delay”, which is required for the modem to lock on to the

incoming data stream and is dependant on the radio signal baud rate. Minimum timings are

given below:

Baud Rate Lead in Delay(Minimum)

150 80ms

300 60ms

600 40ms

1200 40ms

2400 40ms

4800 20ms

9600 30ms

For simplex/semi-duplex operation, time is required for the transmit and receiver synthesiser

to be loaded and locked prior to transmission/reception. This timing constraint is important

when deciding how soon after receiving a message a reply may be sent. For simplex/semi-

duplex operation the ZRT is ready to receive data approximately 25ms after transmission

ceases. It is therefore necessary to either wait this length of time after receiving a message before

sending a reply or to extend the lead in delay by the same amount to hold off transmission of

the data.

For applications where power save is in use the lead in delay should be extended to allow the

receiving device to wake up. The time required can be calculated by adding the save on time to

the save off time and adding 10 percent, e.g. for a save on time setting of 800ms and a save off

time of 200ms the lead in delay should be 1100ms.

Care must be taken when replying to a previously transmitting ZRT when RTS/CTS handshake

is not being used, in this mode the transmitting device will wait for two character times before

turning off its carrier and may therefore miss the beginning of a reply if it comes too soon, this

may be overcome either by imposing an additional two character delay in the controlling device

or by extending the lead in delay by that amount.

The ZRT also has a facility for imposing a lead out delay, which is the time that the carrier

remains on after transmission of the message is complete. This delay can normally be left at

zero as it is only of use where a controller makes use of the DCD signal to suppress data

processing but suffers some delay in processing received data, or where there is a need to delay

any spurious squelch tail characters generated sufficiently that connected equipment does not

confuse them with part of the message.

ZRT Manual Page 23 of 37 Rev. J – 11 September 2008

5.15.1 Receive To Transmit Switching Time

When using the internal modem the action that initiates transmission can be either receipt of a

character at the serial port or the operation of RTS. These examples use the first mode. The radio

does nothing until the stop bit of the first character for transmission has been received, the

transmitter is then started:

The time delay between receipt of the stop bit for the first character to be transmitted at the

transmitting radio and output of the start bit of that character at the receiving radio is the sum

of the values ttxon, tlid, trbyte, and tmdel shown in the diagram above. Values for these

parameters are indicated below:

TABLE A: Timing values for duplex and simplex modes are as follows:

symbol Description Semi-

duplex

simplex

ttxon Time from external action to commencing transmission 9ms 9ms

tlid Duration of synchronisation transmission (lead in delay) Table B Table B

trbyte Duration of 1 byte at radio signal baud rate Table C Table C

tmdel Modem decode latency Table D Table D

TABLE B: The lead in delay is a programmable parameter but minimum values dependant on

baud rate must be adhered to. However, in a scanning system with the base station on

continuous transmit the base station lead in delay can be set for Zero (thereby saving valuable

time) as the internal outstation modems will always be synchronised.

Baud 150 300 600 1200 2400 4800 9600

Min tlid 80ms 60ms 40ms 40ms 40ms 20ms 30ms

TABLE C: The duration of a byte at the radio baud rate is dependant upon the data format

employed, the table below assumes a format of one start bit, 8 data bits, no parity and 1 stop bit,

i.e. a total of 10 bits per character. If another format is used the appropriate correction must be

made.

Baud 150 300 600 1200 2400 4800 9600

trbyte 66.7ms 33.3ms 16.7ms 8.3ms 4.17ms 2.08ms 1.04ms

TABLE D: The modem decode latency takes into account delays introduced by hardware and

software filters. The total delay is baud rate dependant:

Baud 150 300 600 1200 2400 4800 9600

tmdel 6.9ms 3.5ms 1.7ms 1.3ms 1ms 1ms 1ms

ZRT Manual Page 24 of 37 Rev. J – 11 September 2008

5.15.2 Message Duration

The time taken to transmit a message can be simply derived by multiplying the number of

characters in a message by the values given in table C making any appropriate corrections for

data format. The exception is 9600 baud where extra synchronisation sent during the message

must be taken into account, 8 synchronisation bits lasting a total of 0.833ms are sent after

every eighth message character.

5.15.3 Transmit To Receive Switching Time

In full or semi-duplex operation transmit to receive switching time does not need to be

considered as the receive path is maintained during a transmission, in simplex operation some

time must be allowed to reload the transmitter synthesiser to stop it from interfering with the

receiver. The diagram below indicates the minimum time in which the radio is able to receive a

signal after completing a transmission.

symbol Description value

thold Period for which carrier is held up after sending last data

byte

2.5ms + LOD

trxrdy Time to reload transmit synthesiser in simplex mode 6ms

During the time thold the radio transmits some padding bits to allow for propagation delays in

the receiving device before shutting off the carrier, this prevents possible chopping of the

message tail. The time thold is composed of a fixed 2.5ms period plus the programmable value

LOD (lead out delay). LOD is normally set to zero. After the time trxrdy has expired the radio

is ready to receive a new signal.

N.B. If RTS/CTS handshaking is not used the transmitter is turned on whenever data is received at the

serial port, the transmitter is left on until all buffered data has been transmitted and no data has been

input for a time equivalent to the length of two characters at the radio baud rate (refer to table C). In

general data transmitted by the radio is delayed with respect to its receipt at the serial port by the receive

to transmit switching time, if the radio baud rate and serial port baud rate and both data formats are the

same this delay remains constant throughout the transmission. At the higher baud rates this delay is

generally greater than the length of two characters and so the procedure to stop transmission is started as

soon as the last character has been sent, at the lower baud rates however it is possible that the time thold

is extended while the radio waits for the two character timeout to expire, this can also happen if data

characters are not loaded back to back into the serial port.

ZRT Manual Page 25 of 37 Rev. J – 11 September 2008

5.16 POWER CONSUMPTION

The ZRT is a very low power product and is ideal for operation from batteries with solar power

backup. The information below is intended to help the user decide on the best battery and solar

cell size for operation at non powered sites.

5.16.1 Transmitter RF power verses current

TX Power 5W 4W 3W 2W 1W 500mW 200mW 100mW 50mW

Max. Current 2.1A 1.8A 1.6A 1.3A 950mA 675mA 500mA 390mA 300mA

5.17 POWER SAVE MODE

The ZRT is equipped with an internal and external power save mode. These are outlined below:

5.17.1 Internal Power Save

In this mode the microprocessor switches the transceiver off and after a pre-programmed time

(Save on time) switches the unit back on (Save off time). If a carrier is not detected then the

transceiver again switches off. If during the time the transceiver is awake a carrier is received,

the unit will stay on. After the carrier drops out the receiver will stay on until the programmed

resume time elapses. Once the resume time has elapsed the unit will return to its power save

mode. The Save On/Off and Resume time are all programmable via the PC program. Obviously

the amount of power saved increases with the programmed save on/off ratio, however with

power save enabled long lead times must be programmed to wake up the unit before

communication can take place. Therefore it may not be possible to run all applications under

the power save mode due to the turn around times required by the host system. In some

circumstances it is possible to achieve power save and fast polling: If polling of all outstations is

carried out in cycles with a reasonable gap between each cycle, a long initial poll can be used to

wake up all stations, the resume timer will then restart each time an outstation is polled

allowing fast access, when the cycle is complete all stations will return to power save after the

resume time has expired.

5.17.2 External Power Save

Under this mode the on/off ratio is controlled externally via the DTR line (DTR shut down

must first be enabled using the set up program). In this mode more of the modem's circuits are

shutdown (including the microprocessor), this saves more power but care must be taken to

ensure that the modem is enabled when a transmission is to take place. Note that there is a

hardware link option to allow the serial port to shut off when DTR is not active; this allows the

radio current to be reduced to its bare minimum. In applications where DTR is not connected

this link option must of course be disabled.

5.18 “RSSI” RECEIVE SIGNAL STRENGTH INDICATION

The ZRT produces an internal DC signal which is proportional to the received signal strength.

The DC signal is passed to the internal MPU where it accurately measures its value by an

internal A-D converter. The radios are individually calibrated during production so that signal

strength can then be read in dB micro volts on a PC connected to the serial port.

ZRT Manual Page 26 of 37 Rev. J – 11 September 2008

5.19 STATUS LEDS

The ZRT has a number of LEDs to enable the operator to see at a glance the status of the

product and the serial port:-

RX RF Carrier Detect/Busy

TX Transmit

SYS System

RXD Receive Data

TXD Transmit Data

5.19.1 System LED

With the Exception of the System LED the remainder are self explanatory. The System LED

lights when the radio is being programmed and is also used as a quick check as to the status of

the unit. If any alarms are detected it will flash out an Error number.

5.19.2 Error Number

The modem reports errors in two ways, firstly the BUSY led will come on and the SYS led will

flash a number of times, the BUSY led will then go out again and if the fault persists the

procedure will be repeated. An error number can be determined by counting the number of

times the SYS led flashes while the BUSY led is on.

ERROR No FAULT

1Position of the channel switches has changed.

2A channel has been loaded that has no RX frequency programmed.

3Transmission has been attempted on a channel that has no TX frequency

programmed.

4The receiver synthesiser phase locked loop has failed to lock due to bad

channel data or programming of an out range frequency.

5The transmitter synthesiser phase locked loop has failed to lock due to

bad channel data or programming of an out of range frequency.

6The contents of the microprocessor's EEPROM are corrupted (failed

checksum) in the general program area.

7Internal comms with a high power amplifier have failed.

8The contents of the microprocessor's EEPROM are corrupted (failed

checksum) in the calibration area.

9The contents of the microprocessor's EEPROM are corrupted (failed

checksum) in the factory program area.

10 No POCSAG message stored for repeat test.

11 Rotary channel switch position overridden by software.

12 Tx power setting out of range.

13 Packet Mode cycle pointer invalid.

14 Bad routing table area EEPROM checksum.

15 I2C Bus initialisation error.

ZRT Manual Page 27 of 37 Rev. J – 11 September 2008

6STORE & FORWARD

6.1 STORE & FORWARD BASED ON CLIENT PROTOCOL.

To conserve valuable air time and avoid the possibility of collisions due to coverage overlaps

with other repeaters transmitting at the same time, only messages that require forwarding by

specific repeaters are re-transmitted when the ZRT is used in “Store & Forward” mode.

This is achieved by stripping out the addresses of incoming serial messages, comparing the

address with the list of outstation addresses stored in the unit and routing the messages

accordingly. This requires knowledge of the client’s message structure and, specifically, where

the address can be found in the message.

There is normally local communication at the store and forward site, via the RS232 port.

We have written various store & forward drivers to cope with a number of client specific

message formats and are always happy to write new drivers as and when required. Further

information is available from the sales office.

6.2 MODBUS

6.2.1 Setting Up MODBUS Operation

The ZRT can be programmed to transport “MODBUS ASCII” or “MODBUS RTU” format

messages in single master systems. These options are selected as the “INTERFACE

PROTOCOL” in the “EDIT MODE/INTERFACE” menu. It is not necessary for all radios to run

the same Modbus interface, “MODBUS ASCII” and “MODBUS RTU” modes can be mixed

within a system.

When Modbus modes are enabled the “NETWORK ID” and “RADIO ADDRESS” fields must be

filled out such that every radio in a system has the same network ID, but a different radio

address. Notes should be kept detailing the installation of radios and their addresses.

When transporting Modbus messages the master station radio must be programmed with a

routing table. This is accessed in the “EDIT MODEM/INTERFACE” menu by setting

“ROUTING TABLE” to “ON” and selecting “EDIT ROUTING TABLE”. This selection leads to

several pages of Modbus addresses and the route by which every Modbus address is reached

must then be entered, for example if the Modbus device with address 37 is physically connected

to the radio with radio address 23, and radio 23 is accessed from the base station via relay

radios 4 and 19, then the field entitled “MBUS 37” should be loaded with the route “4,19,23”. If

the Modbus devices with Modbus addresses 65 and 93 are physically connected to radio 45 and

no relays are required then the fields entitled “MBUS 65” and “MBUS 93” should both be

loaded with “45”.

6.2.2 MODBUS Operation

Operation in Modbus modes relies on the master/slave poll/reply nature of Modbus. The set

up of the radios does not differentiate between a master and slave, the only difference in

practice would be that the master station radio will be loaded with a routing table. There is no

restriction on the number of masters in a system, but they should all be loaded with routing

tables.

When a poll is initiated at a master station radio the destination Modbus address in the Modbus

message is looked up in the routing table to determine the addresses of the radio(s) required to

complete the link, the message is then sent and all the radios expect to send a reply back the

same way. Once this reply has been sent the radios are all ready to start another poll/reply

sequence.

ZRT Manual Page 28 of 37 Rev. J – 11 September 2008

If a radio is specified as a relay in a link, any locally connected Modbus devices will not be

aware of communications that take place as no activity occurs on the serial port in this state.

This may cause problems however if more than one master exists in a system as a radio that is

being used as a link in a relay is not available to transmit messages.

6.2.3 Power-Save Operation With MODBUS

When Modbus modes are enabled in the configuration programme two further fields appear

entitled “MIN PWR SAVE ADDRESS” and “MAX PWR SAVE ADDRESS”. If power save

operation is not required set both these fields to zero.

If power save operation is required it is enabled by setting the “RADIO ADDRESS” to a value

greater or equal to “MIN PWR SAVE ADDRESS” and less than or equal to “MAX PWR SAVE

ADDRESS”. The radio will then enter low power standby mode for the time programmed in the

“PSAVE ON TIME” field in the main edit menu, it will then wake up and check for an incoming

signal, if none is present it will return to sleep and repeat the cycle. If a signal is detected the

radio will stay awake until a reply to the outward bound message has been returned.

When the master station or relay radios send an outward bound message, the address of the

radio to which the message is being sent is checked against the min and max power save

addresses, if a power saved radio is indicated a cyclic wake up message is sent for the period

indicated by the programmed power save on time before the actual data message is sent, if a

power saved radio is not indicated the data message is sent immediately. These parameters

along with some others are also used to calculate a timeout time in the event that no reply is

received. It is therefore essential that all radios in a system are programmed with the same

parameters even if not power saved, otherwise communications will fail.

Note that if “DTR SHUTDOWN” is enabled a radio remains completely shut down while DTR

is inactive, it will not wake up according to the power save timer to see if any incoming

messages are present. This mode should therefore only be used in conjunction with real time

message scheduling.

6.2.4 Serial Port Handshaking With MODBUS

When Modbus modes are enabled the DTR and DSR signalling lines can be used to assist in

power saving the host Modbus device. The RTS and CTS lines are not used and the “RTS/CTS

HANDSHAKE” option in the “EDIT MODEM/INTERFACE” menu of the WinA4P programme

should be set to “OFF” in RS232 versions. When the Modbus slave is ready to accept data it

should assert DTR, DSR will be asserted in response and the received message will be output to

the Modbus device. The “HOST INACTIVITY TIME” field in the set up programme defines a

time limit for the Modbus device to assert DTR in response an incoming message and if this

time limit is exceeded the radio sends back a reply indicating the destination device failed to

respond and the link is cancelled. After sending a response, the Modbus slave may then release

DTR and return to power save mode. Note that as long as DTR is asserted the radio will not

return to its power save mode (if enabled in the setup programme). DSR will remain asserted in

this case.

The master station can also control the power saving of its radio using DTR, the radio will

operate in power save mode as long as DTR is not active, asserting DTR wakes the radio, DSR

is asserted in return to indicate that the radio is awake and ready to accept data.

If use of the handshake lines is not required DTR should be connected to a voltage of +3.5 to

+15V such that sleep mode is never allowed.

ZRT Manual Page 29 of 37 Rev. J – 11 September 2008

6.2.5 Timeouts in MODBUS Modes

When a transmission from a master station radio is made in Modbus mode the radio will

calculate a timeout for a reply, this calculation is based on many configuration parameters

including the radio baud rate, lead in delay, host inactivity time, maximum message length,

power save timing etc. If power saving is enabled and the baud rate is low this time can be large

(the calculation limits the result to a maximum of 4.25 minutes. To reduce the possibility of

“hung” radios the destination radio will send a link closing message if the destination Modbus

slave does not reply. This link closing message is only used by the radios to close the link, it is

not passed to the Modbus master.

If the Modbus master itself times out before the radio link does, it can send another poll, radios

along the link will cancel the previous route and set up the new one. The exception to this is the

previous destination radio if it is still trying to wake up its Modbus slave, it will ignore the new

message and try to download its original message when the slave awakes, a conflict will then

arise if a reply is sent. To avoid this situation the Modbus master timeout time should allow the

maximum “HOST INACTIVITY TIME” to expire plus the time required to get a message and its

reply through the link.

6.3 RFT ROUTING PROTOCOL

6.3.1 Setting Up RFT Routing Operation

The ZRT can be programmed to route non-specific protocol messages in single master systems

using “RFT ROUTING” mode. This mode supports relay messaging. This option is selected as

the “INTERFACE PROTOCOL” in the “EDIT MODEM/INTERFACE” menu.

In describing operation the address contained in the host system message will be referred to as

the “protocol address” and address programmed in the radio under the “RADIO ADDRESS”

field in the setup program will be referred to as the “radio address”.

RFT Routing mode is controlled at the master station by picking out an 8 bit protocol address

field in the message to be sent, this address is then looked up in the routing table stored in the

master station radio. The routing table can contain the radio address (as programmed in the

RADIO ADDRESS field in the setup program) of a single radio connected to the required

destination device or a list of relay radio addresses plus the destination radio address. The

message is then transmitted from the base station radio as a packet with the routing information

prefixed to it. The message is then relayed through any relay radios specified until it reaches the

destination radio where it is output from the serial port in its original form with the packet

information removed. During this process each radio considers itself to be part of an established

link. A reply is then expected, however the outstation radios are not programmed with routing

tables, a reply issued is assumed to be destined to the master station. The address in the

protocol message is therefore not checked and the reply is simply sent back down the

established link to the master station radio where it is output from the serial port. As the reply

is passed back the link members no longer consider themselves to be part of an established link

and return to idle.

Note that there is no differentiation in operating mode between a relay radio and an outstation

radio, if an outstation radio is specified as a relay in a link any device connected to the local

serial port will be unaware of relay communications taking place.

The packet used to transfer protocol messages specifies the route to be taken and also the

current stage in the route, it is therefore of no concern if radios further down a relay link “hear”

the message before they are expected to repeat it, they will ignore the message until specifically

requested to repeat it.

ZRT Manual Page 30 of 37 Rev. J – 11 September 2008

The position of the address in the protocol field is specified using the “ADDRESS OFFSET”

parameter in the setup programme. A setting of 0 specifies zero offset, i.e. the address is the first

byte in the message, an offset of 6 specifies the 7th message byte and so on. 16 bit addressing or

more is not supported as a maximum of only 256 destinations can be supported by the routing

table. If the protocol message format does use 16 bit addressing specify the offset for the least

significant byte and try to ensure that no two devices use the same l.s.b. in their address.

In order to determine the position of the address in a protocol message the radio has to know

where the message starts and ends, this can be done in one of two ways: If the RTS/CTS

HANDSHAKE option is turned on (option only available in RS232 Full Handshaking and 5V

TTL radio versions), RTS should be activated before commencing a message, CTS will be

activated in response and the message may be loaded. The first character received after CTS

becomes active is considered to be the start of the message. Transmission will start as soon as

enough characters have been loaded for the protocol address to be extracted and the route

determined from the routing table. Transmission continues until RTS is de-activated, CTS will

drop when transmission is complete. CTS may also drop if the serial input buffer becomes more

than ¾ full to implement flow control, if this happens RTS should be kept active until CTS is re-

activated, more characters may then be loaded or RTS may be dropped.

If the RTS/CTS HANDSHAKE option is turned off or is not an available option, the radio relies

on gaps in the serial data to determine the start and end of messages. A gap equivalent to two

character periods at the serial port baud rate is treated as a message end. The first character

received after such a gap is treated as the first character of the next message.

When RFT ROUTING mode is enabled the “NETWORK ID” and “RADIO ADDRESS” fields

must be filled out such that every radio in a system has the same network id, but a different

radio address. Notes should be kept detailing the installation of radios and their addresses.

The master station radio must be programmed with a routing table, this is accessed in the

“EDIT MODEM/INTERFACE” menu by setting “ROUTING TABLE” to “ON” and selecting

“EDIT ROUTING TABLE”. This selection leads to several pages of protocol addresses, the route

by which every protocol address is reached must then be entered, for example if the device with

protocol address 37 is physically connected to the radio with radio address 23, and radio 23 is

accessed from the base station via relay radios 4 and 19, then the field entitled “ADDR 37”

should be loaded with the route “4,19,23”. If the devices with protocol addresses 65 and 93 are

physically connected to radio 45 and no relays are required then the fields entitled “ADDR 65”

and “ADDR 93” should both be loaded with “45”.

6.3.2 Power-Save Operation With RFT Routing

When RFT ROUTING mode is enabled in the configuration programme two further fields

appear entitled “MIN PWR SAVE ADDRESS” and “MAX PWR SAVE ADDRESS”, if power

save operation is not required set both these fields to zero.