Microhard Systems 01P5 MHX-920 SST Module User Manual MHX920manual

Microhard Systems Inc MHX-920 SST Module MHX920manual

Manual

Operating ManualMHX-920900 MHz Spread Spectrum OEM TransceiverRevision 1.20, December 21, 2000Microhard Systems Inc.#110, 1144 - 29th Ave. N.E.Calgary, Alberta T2E 7P1Phone: (403) 248-0028Fax: (403) 248-2762www.microhardcorp.com
ii MHX-920 Operating ManualMHX-920900 MHzSpread-SpectrumEmbedded ModemWARNINGIn order to comply with the FCC/ICadopted RF exposure requirements, thistransmitter system will be installed by themanufacturer's reseller professional.Installation of all antennas must beperformed in a manner that will provide atleast 23 cm clearance from the frontradiating aperture, to any user or memberof the public.EQUIPMENT LABELINGThe manufacturer, product name, and FCCand Industry Canada identifiers of thisproduct must appear on the outside label ofthe end-user equipment.lThis manual contains information of proprietary interest toMicrohard Systems Inc. It has been supplied in confidence topurchasers and users of the MHX-920, and by accepting thismaterial the recipient agrees that the contents will not be copiedor reproduced, in whole or in part, without prior written consentof Microhard Systems Inc.Microhard Systems Inc. has made every effort to assure that thisdocument is accurate and complete. However, the companyreserves the right to make changes or enhancements to themanual and/or the product described herein at any time andwithout notice. Furthermore, Microhard Systems Inc. assumesno liability resulting from any omissions in this document, orout 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 inapplications where failure could result in damage to property orhuman injury or loss of life.The electronic equipment described in this manual generates,uses, and radiates radio frequency energy. Operation of thisequipment in a residential area may cause radio interference, inwhich case the user, at his own expense, will be required to takewhatever measures necessary to correct the interference.FCC Declaration of ConformityThis device complies with Part 15 of the FCC Rules.Operation is subject to the following two conditions: (1) thisdevice may not cause harmful interference, and (2) thisdevice must accept any interference received includinginterference that may caused undesired operation.Microhard Systems Inc.’s products are warranted against allfailures which occur as a result of defective material orworkmanship within 12 months of purchase by the user. Thiswarranty does not extend to products that, in the opinion ofMicrohard Systems Inc., have been subject to misuse, accidents,lightning strikes, improper installation or application, nor shallit extend to units which have, in Microhard Systems Inc.’sopinion, been opened, tampered with or repaired by anunauthorized facility.Microhard Systems Inc.Leaders in Wireless Telecom#110, 1144 - 29th Ave. N.E.Calgary, Alberta T2E 7P1Phone: (403) 248-0028Fax: (403) 248-2762www.microhardcorp.com© 2000 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 registeredtrademarks of their respective holders.Manual Revision 1.20, December 21, 2000.
iii MHX-920 Operating ManualContents1. Introduction1.0 Product Overview .............................................................................................................................................................................. 11.1 Features.............................................................................................................................................................................................. 11.2 About this Manual ............................................................................................................................................................................. 22. Electrical/Physical2.0 Functional Block Diagram................................................................................................................................................................. 32.1 Pinout................................................................................................................................................................................................. 42.2 LED Operation................................................................................................................................................................................... 62.3 DC Characteristics............................................................................................................................................................................. 82.4 AC Characteristics.............................................................................................................................................................................. 93. Modes of Operation ..................................................................................................................................................................................... 113.1 Data Mode ........................................................................................................................................................................................ 113.2 Command Mode ............................................................................................................................................................................... 123.2.1 AT Command Interface ....................................................................................................................................................... 133.3 Switching Between Command and Data Modes............................................................................................................................... 134. Configuration4.1 Quick Start Approach ...................................................................................................................................................................... 154.2 AT Commands................................................................................................................................................................................. 16A - Answer........................................................................................................................................................................................ 17E - Command Echo.......................................................................................................................................................................... 17I - Identification ............................................................................................................................................................................... 17O - Online Mode.............................................................................................................................................................................. 17Q - Quiet Mode................................................................................................................................................................................ 17V - Result Codes Display................................................................................................................................................................. 17W - Connection Result..................................................................................................................................................................... 18Z - 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............................................................................................................................................. 19Sxxx? - Read S register value........................................................................................................................................................... 19Sxxx=yyy - Set S register value ....................................................................................................................................................... 19Command Result Codes................................................................................................................................................................... 204.3 S Registers ....................................................................................................................................................................................... 21S Register 2 - Escape Code............................................................................................................................................................... 21S Register 3 - CR Control Code....................................................................................................................................................... 21S Register 4 - Linefeed Control Code .............................................................................................................................................. 21S Register 5 - Backspace Control Code ........................................................................................................................................... 21S Register 101 - Operating Mode..................................................................................................................................................... 22S Register 102 - Serial Baud Rate.................................................................................................................................................... 24S Register 103 - Wireless Link Rate ................................................................................................................................................ 24S Register 104 - Network Address................................................................................................................................................... 25S Register 105 - Unit Address.......................................................................................................................................................... 25S Register 106 - Primary Hopping Pattern....................................................................................................................................... 25S Register 206 - Secondary Hopping Pattern.................................................................................................................................... 25S Register 107 - Encryption Key...................................................................................................................................................... 27S Register 108 - Output Power Level............................................................................................................................................... 27S Register 109 - Hopping Interval.................................................................................................................................................... 28S Register 110 - Data Format............................................................................................................................................................ 29S Register 111 - Packet Minimum Size ............................................................................................................................................ 29S Register 112 - Packet Maximum Size............................................................................................................................................ 29S Register 114 - Packet Size Control ................................................................................................................................................ 29S Register 116 - Packet Character Timeout ...................................................................................................................................... 29S Register 113 - Packet Retransmissions.......................................................................................................................................... 30S Register 213 - Packet Retry Limit.................................................................................................................................................. 31S Register 115 - Packet Repeat Interval........................................................................................................................................... 31S Register 117 - Modbus Mode ........................................................................................................................................................ 32S Register 118 - Roaming................................................................................................................................................................. 33S Register 119 - Quick Enter to Command....................................................................................................................................... 33
iv MHX-920 Operating ManualS Register 120 - RTS/DCD Framing................................................................................................................................................. 33S Register 121 - DCD Timeout......................................................................................................................................................... 33S Register 122 - Remote Control ...................................................................................................................................................... 34S Register 123 - RSSI Reading......................................................................................................................................................... 344.4 Diagnostics, Statistics and Remote Control...................................................................................................................................... 354.4.1 Spectrum Analyzer Feature............................................................................................................................................................... 354.4.2 Statistics............................................................................................................................................................................................ 354.4.3 Remote Control and Diagnostics ...................................................................................................................................................... 365. Installation ................................................................................................................................................................................................... 395.1 Estimating the Gain Margin.............................................................................................................................................................. 395.2 Antennas and Cabling....................................................................................................................................................................... 415.2.1 Internal Cabling ................................................................................................................................................................................ 415.2.2 Installing External Cables, Antennas and Lightning Arrestors.......................................................................................................... 42A. Modem Command Summary...................................................................................................................................................................... 45B. Serial Interface............................................................................................................................................................................................ 47C. Sample Schematic Diagram........................................................................................................................................................................ 49D. Factory Default Settings.............................................................................................................................................................................. 51EPerformance Tables...................................................................................................................................................................................... 53F. Hopping Tables............................................................................................................................................................................................ 55G. Technical Specifications............................................................................................................................................................................. 57H. Mechanical Drawing.................................................................................................................................................................................... 59I. Glossary ...................................................................................................................................................................................................... 61
MHX-920 Operating Manual: Chapter 1 Introduction. 11. Introduction1.0 Product OverviewThe MHX-920 is a high-performance embedded wireless data transceiver.Operating in the 902 - 928 MHz ISM band, this frequency-hopping spread-spectrum module is capable of providing reliable wireless data transferbetween almost any type of equipment which uses an asynchronous serialinterface. The small-size and superior RF performance of this module makeit ideal for many applications. Typical uses for this module include:n SCADAn Traffic Controln Remote Monitoringn Fleet Management;n Telemetry;n Remote Camera/Robot Control;n Security Systems; and,n Display Signs.While a pair of MHX-920 modules can link two terminal devices (“point-to-point” operation), multiple modules can be used together to create a networkof various topologies, including “point-to-multipoint” and “repeater”operation. Multiple independent networks can operate concurrently, so it ispossible for unrelated communications to take place in the same or a nearbyarea without sacrificing privacy or reliability.1.1 FeaturesKey features of the MHX-920 include:ntransmission within a public, license-exempt band of the radiospectrum1 – this means that it can be used without access fees(such as those incurred by cellular airtime);na serial I/O data port with handshaking and hardware flowcontrol, allowing the MHX-920 to interface directly to anyequipment with an asynchronous serial interface. 1902-928 MHz, which is license-free within North America; may need to be factory-configureddifferently for some countries.
2MHX-920 Operating Manual: Chapter 1 Introductionn64 sets of user-selectable pseudo-random hopping patterns,intelligently designed to offer the possibility of separatelyoperating multiple networks while providing security, reliabilityand high tolerance to interference;nencryption key with 65536 user-selectable values to maximizesecurity and privacy of communications;nbuilt-in CRC-16 error detection and auto re-transmit to provide100% accuracy and reliability of data;nease of installation and use – the MHX-920 module uses asubset of standard AT style commands, very similar to thoseused by traditional telephone line modems.While the typical application for the MHX-920 is to provide a short- to mid-range wireless communications link between DTEs, it can be adapted toalmost any situation where an asynchronous serial interface is used and dataintercommunication is required.1.2 About this ManualThis manual has been provided as a guide and reference for installing andusing MHX-920 wireless modem modules. The manual contains instructions,suggestions, and information which will help you set up and achieve optimalperformance from your equipment using the MHX-920 module.It is assumed that users of the MHX-920 module have either systemintegration or system design experience. Chapter 2 details theelectrical/physical attributes of the module. Chapter 3 explains the differentmodes of operation. Chapter 4 provides complete details of all configurationparameters; and, Chapter 5 is an installation/deployment guide. TheAppendices, including the Glossary of Terms, are provided as informationalreferences which you may find useful throughout the use of this manual aswell as during the operation of the wireless modem.Throughout the manual, you will encounter not only illustrations that furtherelaborate on the accompanying text, but also several symbols which youshould be attentive to:Caution or Warning: Usually advises against some action which couldresult in undesired or detrimental consequences.Point to Remember: Highlights a key feature, point, or step which is worthnoting, Keeping these in mind will make using the MHX-920 more usefulor easier to use.Tip: An idea or suggestion is provided to improve efficiency or to makesomething more useful.With that in mind, enjoy extending the boundaries of your communicationswith the MHX-920 module.
MHX-920 Operating Manual: Chapter 2 Electrical/Physical 32. Electrical/Physical2.0 Functional Block DiagramAntennaSwitchMixerLNAMixerIF DemodFrequencySynthesizerPAComparator+-uC8 bit data busUART(DCE)GAINA/D SRAM EEPROMSRAMCTSDCDDSRRxDDTRTxDRTS\Config\ResetRSSI1-3RXMODETXMODEDVccAVccGNDFigure 1. Functional Block Diagram
4MHX-920 Operating Manual: Chapter 2 Electrical/Physical2.1 PinoutFigure 2 provides a top-view pinout drawing of the MHX-920 module. Thecorner pins (1,20,21,40) are labeled directly on the module.12345678910111213141516171836353433323130292827262524232221AVccAVccDVccDVccDVccDVccDVccNC\Config\ResetGNDGNDGNDGNDGNDGNDGNDNCNCNCNCNCNCNCNCRx/SYNCTxMODERSSI3RSSI2RSSI1CTSRTSDSRNCDTRTxDMHX-9101920NCNCRxDDCD37383940Figure 2 - Pinout (Top View)Table 1. Pin DescriptionPin Name No. Description I/OAVcc 1,2 Positive Supply for Radio Circuitry. See Section2.3 for DC Characteristics I\Config 9Leave unconnected. For factory use only. Donot groundCTS 28 RS-232 Clear to Send. Active low (TTL level)output. See Appendix B for a complete descriptionof all RS-232 signals.ODCD 21 RS-232 Data Carrier Detect. Active low (TTLlevel) output. ODSR 26 RS-232 Data Set Ready. Active low (TTL level)output. ODTR 24 RS-232 Data Terminal Ready. Active low(TTL level) input.IDVcc 3-7 Positive Supply for Logic circuitry and I/Opins. See Section 2.3 for DC CharacteristicsI
MHX-920 Operating Manual: Chapter 2 Electrical/Physical 5Table 1 (continued)GND 11-17 Ground reference for logic, radio and I/O pins.\Reset 10 Active low reset input to the module. SeeSection 2.4 for timing information.IRSSI1 29 Receive Signal Strength Indicator 1. Thisoutput is the first of the three RSSI indicatorsto become active high as the signal strengthincreases. See Section 2.2 for detailsORSSI2 30 Receive Signal Strength Indicator 2. Thisoutput is the second RSSI indicator to becomeactive high as the signal strength increases.See Section 2.2 for details.ORSSI3 31 Receive Signal Strength Indicator 3. Thisoutput is the last RSSI indicator to becomeactive high as the signal strength increases.See Section 2.2 for details.ORTS 27 RS-232 Request to Send. Active low (TTLlevel) input.IRxD 22 RS-232 Receive Data. TTL level output. ORX/SYNC 33 Active high output indicates receive andsynchronization status. See Section 2.2.OTxD 23 RS-232 Transmit Data. TTL level input. ITXMODE 32 Active high output indicates module istransmitting data over the RF channel. SeeSection 2.2.O
6MHX-920 Operating Manual: Chapter 2 Electrical/Physical2.2 LED OPERATIONLED 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 OperationLEDMODE RX/Sync TXMode RSSI1,2,3Power Up (S0=1, S119=1) off off blink 500mson/500ms offPower Up (S0=1, S119=0) off off offPower Up (S0=0) off off offCommand Mode off off offData Mode - Master on while receivingvalid data packetsfrom slaves andrepeaters in thenetworkon for the firstportion of eachhop interval.RSSI modebased on allreceived packetsSee Table 3Data Mode - RepeaterDuring Sync. Acquisition off off alternating300ms onData Mode - RepeaterWhen Synchronized on for first portionof hop interval on for secondportion of hopintervalRSSI modebased on packetsreceived fromSlaves*See Table 3Data Mode - Slave DuringSync. Acquisition off off alternating300ms onData Mode - SlaveWhen Synchronized on on whentransmitting apacket.RSSI modebased on packetsreceived from theRepeater orMaster withwhich itcommunicatesSee Table 3*If Slaves have been silent for 2 seconds, repeater will base its RSSI onpackets received from the Master.
MHX-920 Operating Manual: Chapter 2 Electrical/Physical 7Signal strength, which is also reported in Register S123, is calculated basedon the last four valid received packets with correct CRC, and represented byRSSI1, 2 and 3.For slaves, packets are received on every single hop either from a repeater, orthe master.When calculating RSSI, the master takes into consideration all packetsreceived from slaves and repeaters. Repeaters and slaves only transmit backto the master when they have information to send. Therefore, if no data iscoming back to the master then RSSI will never get updated at the master,and the LED’s will be off.Table 3 - RSSI mode operationSignal 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
8MHX-920 Operating Manual: Chapter 2 Electrical/PhysicalIMPORTANT:For best performance, it isstrongly recommended to usea separate, linearly regulatedsupply for Vcc Radio. Donot directly feed a switchingpower supply into VccRadio.For OEM design simplicity,connect both the radio andlogic Vcc connectionstogether.Caution: Using any other powersupply which does not provide theproper voltage or current coulddamage the MHX-920 module.2.3 DC CharacteristicsSym Characteristic Min Typ Max UnitsAVCC Radio Supply Voltage 4.9 5.0 5.5 VDVCC Logic Supply Voltage 4.75 5.0 5.5 VVPOT Power On Reset Threshold Voltage 1.8 22.2 VVRST Reset Pin Threshold Voltage DVCC/2VAICCR Radio Supply Current in Receive Mode 96 107 117 mAAICCT0Radio Supply Current at 1mW Transmit 68 108 119 mAAICCT1Radio Supply Current at 10mW Transmit 111 123 135 mAAICCT2Radio Supply Current at 100mW Transmit 157 174 191 mAAICCT3Radio Supply Current at 1W Transmit 398 442 486 mADICC Logic Supply Current 95 105 115 mAVIL Input Low Voltage (Pins 23,24,27) -0.5 .3DVCC VVIH Input High Voltage (Pins 23,24,27) 0.6VCC VCC+.5 VVOL Output Low Voltage (Pins 21,22,26,28-33) 0.6 VVOH Output High Voltage (Pins 21,22,26,28-33) 4.2 VISRCESourcing Current (Pins 21,22,26,28-33) 10 mA
MHX-920 Operating Manual: Chapter 2 Electrical/Physical 92.4 AC CharacteristicsSym Characteristic Min Typ Max UnitsTTOUT Reset Delay Time-Out Period 500 msTR2D Internal Reset to Data Mode* 0 5 sTR2C Internal Reset to Command Mode 0ms*Unit will enter into Command Mode upon power up if register S0=0. Unit will enter into DataMode upon power-up if register S0=1. When powering up into Data Mode, an additional delayof 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 \Resetline operation. A fixed internal reset delay timer of roughly 500ms istriggered as the VPOT or VRST threshold is reached.TVVDV\ResetInternal ResetCCTOUTRSTPOTTData ModeR2DTCommand ModeR2C(Valid when S0=1)(Valid when S0=0)Figure 3. Reset Timing
10 MHX-920 Operating Manual: Chapter 3 Modes of Operation
MHX-920 Operating Manual: Chapter 3 Modes of Operation 113. Modes of OperationThe MHX-920 modem can be easily configured to meet a wide range ofneeds and applications. The module is designed such that all communicationis through one serial port (Pins 21 to 28 on the module). This port has twofunctions:1. It provides the asynchronous interface with the host equipment for datathat 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. Whenoperating 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 ofoperation called diagnostics mode. The module will always be in one ofthese three modes.3.1 Data ModeData mode is the normal operating mode of the MHX-920. When in datamode, the MHX-920 is communicating with other MHX-920 modules, andfacilitating wireless asynchronous serial communication amongst two or moreterminal devices. There are three basic elements to any MHX-920communications network:• One module configured as the Master• Zero or more modules configured as Repeaters• One or more modules configured as SlavesThe function of the Master is to provide synchronization for the entirenetwork, and to control the flow of data. There is always one Master pernetwork. The Master is the ultimate destination for all data collected at thevarious Repeater’s and Slave’s serial ports. With the network set up forPoint-to-Multipoint communication, all data received at the Master’s serialport is transmitted to every Repeater and Slave in the network. The MHX-920 is a frequency hopping transceiver, meaning that it “hops” to a newfrequency after a predetermined time interval. This time interval is a fixedtime set by the user, and can range from 8ms to 120ms. The MHX-920 hopsaccording to a pseudorandom pattern of 50 different channels.When configured as a Slave, the MHX-920 searches for synchronization witha Master. Network topologies consisting of a single Master and virtually anycombination of Slaves and Repeaters may be deployed. The functionality ofany particular MHX-920 can be configured as follows:
12 MHX-920 Operating Manual: Chapter 3 Modes of OperationMSNetwork 1MSRMSRNetwork 2MSSSNetwork 3MRSSSNetwork 4MRSRSNetwork 5Figure 4 - Sample NetworkTopologies. Virtually anyCombination of Slaves andRepeaters May be Used.nMaster Point-to-Point: The modem is configured tocommunicate with a single Slave, either directly, or through oneor more Repeaters.nMaster Point-to-Multipoint: The modem is configured tocommunicate with one or more Slaves and/or Repeaters.nSlave: The modem is configured to communicate with oneMaster either directly or through one or more Repeaters..nRepeater: The modem is configured to pass information fromeither a Master or another Repeater onto subsequent Repeatersand/or Slaves and vice versa. The Repeater also acts as a Slavein the sense that, like a Slave, it passes information to/from itsserial port.Examples of different network topologies are shown in Figure 4. Network 1shows Point-to-Point communication between a Master and Slave. Network2 makes use of a Repeater to communicate with the Slave. Network 3illustrates a simple Point-to-Multipoint network with no Repeaters. Networks4 and 5 gives examples of Point-to-Multipoint networks consisting of bothRepeaters and Slaves. There is effectively no restriction to the number ofRepeaters and Slaves that can be added to a network. As seen in Network 4,a Master can communicate directly with both Slaves and Repeaters.3.2 Command ModeThe MHX-920 firmware has been designed to allow the user to customize theoperation of the modem through an AT Command Interface. This interface isideal for direct interface with another microcontroller or for higher levelWindows-based software applications, but also contains user-friendly built-inregister descriptions. These descriptions make it easy for the user toconfigure the unit by manually inputting AT Commands and modifying S-Register parameters, using any standard terminal program. The MHX-seriesdevelopment board is a useful tool for familiarizing yourself with the variousoperating parameters and user interface. Reference schematics for thedevelopment board can be found in Appendix G. To access the MHX-920’scommand mode using the development board:1. Insert the module into the socket with the antenna connector towards theedge of the board.2. Attach the supplied antenna.3. Connect a straight through serial cable between the DB9 connector andthe serial port on your PC4. Run any terminal application program such as Hyperterminal5. Set the serial port to 9600 baud, 8N16. Apply power to the development board7. While the three RSSI LED’s are blinking, type ‘mhx’ (you have about 5seconds to do this). The modem should respond with ‘OK’.8. Type ‘AT&V <ENTER>’
MHX-920 Operating Manual: Chapter 3 Modes of Operation 133.2.1 AT Command InterfaceAt 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=8Operating Mode S101=1 Serial Baud Rate S102=7Wireless Link Rate S103=2 Network Address S104=1Unit Address S105=1 Hop Pattern S106=0Encryption Key S107=1 Output Power S108=2Hop Interval S109=4 Data Format S110=1Packet Min Size S111=1 Packet Max Size S112=43Packet Retransmissions S113=1 Quick enter to command S119=1Packet Repeat Interval S115=1 Character Timeout, ms S116=8RTS/DCD Framing, ms S120=0 DCD Timeout, ms S121=0Secondary Hop Pattern S206=2 Packet Retry Limit S213=2Average RSSI value S123= -0 dBm Modbus Mode S117=0Roaming S118=0 Packet Size Control S114=0Remote Control S122=0OKThe MHX-920 is controlled through an AT Command line interface using acommand set which is very similar to a traditional Hayes telephone modemcommand 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 thebeginning of each command line. For example, to change the operatingmode, type:ATS101=2 <ENTER>The modem should respond with ’OK.’ The above command will set theoperating 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 Modewould revert to its previous value. To store any recently updated commandregisters, the following “write” command must be entered.AT&W <ENTER>3.3 Switching Between Command and Data ModesYour modem must be in command mode for it to execute a command. Ifyou send characters when the modem is in data mode, the modem transmitsthe characters over the air.Depending on its settings, the modem will either power up in command modeor data mode. Normally, when first received from the factory, the unit willpower up into data mode. During the first five seconds after power-up, theuser is given the opportunity to avoid entering into data mode but insteadenter into command mode by typing ‘mhx’.
14 MHX-920 Operating Manual: Chapter 3 Modes of OperationDATAMODEPOWER-UPSEQUENCECOMMANDMODEUSER TYPES 'mhx'5 sec elapsesorcharactersother than 'mhx'entered by the user(ATA or ATO Command) DTR or Escape SequenceFigure 5A. S0=1, S119=1(factory default)DATAMODEPOWER-UPSEQUENCECOMMANDMODE500 msec(ATA or ATO Command) DTR or Escape SequenceFigure 5B. S0=1, S119=0DATAMODEPOWER-UPSEQUENCECOMMANDMODE500 msec(ATA or ATO Command) DTR or Escape SequenceFigure 5C. S0=0The escape sequence will notbe accepted unless both theMHX-920 and the terminalare set to the same baud rateThe terminal must be set for 9600 baud 8N1 in order for the modem to acceptthese characters. If ‘mhx’ is typed incorrectly, the modem will immediatelyenter into data mode. If the five seconds elapses without any response fromthe user, the modem will go into data mode.In command mode, the module “autobauds,” meaning that it will adapt to thebaud rate of the DTE equipment to which it is connected. Therefore, when incommand mode, you may change the baud rate of your equipment, and theMHX-920 will automatically adjust to this baud rate once an AT string isissued. The new baud rate is stored in register S102. Several baud ratesranging from 2400 to 115200 may be selected.You can place the modem into Data Mode from Command Mode either by:• Issuing the answer command (ATA <ENTER>); or,• Issuing the online command (ATO <ENTER>).The modem will now attempt to communicate with other MHX-920 modules.While in Data Mode, the modem will communicate through the serial port atthe same baud rate as was last used in Command Mode2.To return to Command Mode, you can either:• Send the escape sequence. (The escape sequence consists of 1 second ofinactivity, followed by the characters ‘+++’ followed by another secondof inactivity.); or,• Toggle the DTR line (depending on the &D parameter see pg 11).The escape sequence must be issued at the baud rate that the modem has beenset to. If the modem is set to 19200 baud, and the escape sequence is issuedat 9600 baud, for example, the modem will not recognize it, and will not gointo Command Mode.Figure 5 provides a state diagram for power-up, command mode, and datamode. Note that there are three different variants of the state diagram whichdepend on the values of registers S0 and S119. See the appropriate sectionsfor more details about these registers. The factory defaults are S0=1 andS119=1. 2 It is possible to enter into Data Mode at a different baud rate from what iscurrently 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 thebaud rate in this manner. If you issue another AT string after attempting toset the baud rate using ATS102 <ENTER>, the modem will again autobaudand 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 modemto run at 19200 baud, the following command line entry would be suitable:ATS102=5&WA <ENTER>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 modeminto Data Mode. Once in Data Mode, the modem is unable to autobaud, andis fixed at 19200 baud. By combining several commands into one commandline entry, and then immediately putting the modem online, the modem is notgiven a chance to autobaud back to 9600.
MHX-920 Operating Manual: Chapter 4 Configuration 154. ConfigurationWarning: After testing the unitsfor correct operation using thequick-start approach, be sure tomodify some of the securityparameters such as NetworkAddress and Encryption Key, toavoid unintentionalcommunication with other users ofMHX-920 products..MSNetwork 1MSRMSRNetwork 2Figure 6. Basic NetworksThis chapter provides a detailed description of the various operatingparameters of the MHX-920. Section 4.1 provides a quick-start approachwhich outlines the minimum requirements for establishing communicationbetween two MHX-920 modules. The settings will not necessarily provideoptimal performance for your application, but will verify that the modules arefunctioning correctly.Section 4.2 describes the AT Command interface, and the various ATCommands. Section 4.3 covers all S-Register parameters which affect theoperation of the modem, and Section 4.4 provides a description of alldiagnostic features of the modem.4.1 Quick Start ApproachThere are several parameters that must be set in order to establishcommunication between a pair of MHX-920 modules.The MHX-920 is equipped with four standard factory default settings.Instead of manually configuring each individual operating parameter, a globalcommand may be used to quickly configure the modem for a particular typeof operation. For example, to quickly implement Network 1, Factory default1 would be applied to the Master, and Factory default 2 would be applied tothe 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 getyou started and only ensure that a link can be established, but do notnecessarily provide the best performance. Optimization of thecommunications 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 antennaconnector towards the edge of the board.2. Attach the supplied antenna.3. Connect a straight through serial cable between the DB9 connector andthe serial port on your PC4. Run any terminal application program such as Hyperterminal and set theterminal application’s serial port settings to 9600 baud, 8N15. Apply power to the development board6. While the three RSSI LED’s are blinking, type ‘mhx’ (you have about 5seconds to do this). The modem should respond with ‘OK’.7. Configure the unit to Factory Setting 1 by typing AT&F1 <return>. This putsthe unit into Master Point-to-point mode.8. Store these settings to memory by typing AT&W <return>.9. Put the modem into Data Mode by typing ATA (or ATO) <return>10. Perform above steps for the second unit, using Factory Setting 2 instead ofFactory Setting 1. This will configure the second unit as a Slave.
16 MHX-920 Operating Manual: Chapter 4 ConfigurationThe escape sequence will notbe accepted unless both theMHX-920 and the terminalare set to the same baud rateThe units should now be communicating. Remember, the parameters definedby Factory Settings 1 and 2 will likely not be the most ideal for yourapplication, but will quickly allow you to test the units. A complete summaryof the settings defined by all four factory settings can be found in AppendixC. Factory Default Settings.Settings are not immediately stored in non-volatile memory, therefore, thecommand &W is issued to store the current configuration into non-volatilememory. Settings are retained even after powering down. All user selectableparameters for the MHX-920 are described in detail in Sections 4.2 and 4.3:Checking the LinkTo check if the units are communicating, observe the LED indicators on thedevelopment board which houses the Slave unit. If the link is good, up tothree RSSI LEDs on the Slave modem should be active along with theRX/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” orinactive. 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 arereceived at the Master modem. As data is sent from Slave to Master, the RXindicator should blink on as correct packets of data are received. At thispoint, the Master’s RSSI LED’s should become active. It is recommendedthat if the MHX-920 will be deployed in the field where large distancesseparate the units, the modems should be configured and tested in closeproximity (e.g., in the same room) first to ensure a good link can beestablished and settings are correct. This will facilitate troubleshooting,should problems arise.4.2 AT CommandsSeveral AT Commands are supported by the MHX-920. These commandsaffect the operation of the modem in command mode and the transitionbetween data and command modes. More commands and S-Register settingsare discussed in Sections 4.3 and 4.4.To make the command line more readable, you can insert as many spaces asdesired. The command line holds up to 16 characters, not including the ATprefix. If you want to send more than one command line, wait for a responsebefore entering the AT prefix at the start of the next command line.To re-execute the previous command, enter A/. The modem will execute theprevious command line.When in Command Mode, the modem “autobauds”, meaning that it willautomatically adjust to the baud rate of the terminal. You may change theterminal baud rate while in Command Mode without losing communicationwith the modem.For the AT command protocol, an escape sequence consists of threeconsecutive escape codes preceded and followed by at least 1 second ofinactivity. Typically, the ‘+’ character is used as the escape code.+++ preceded and followed by 1 second of inactivity
MHX-920 Operating Manual: Chapter 4 Configuration 17Note that the terminal must be configured to the same baud rate as themodem in order for the modem to recognize the escape sequence. Themodem is unable to “autobaud” while in Data Mode.The following is a description of all available commands. ‘*’ denotesstandard factory settings. All of the following commands must be precededby “AT”.AAnswerThe A command puts the modem into data mode, where the modem attemptsto communicate with other compatibly configured modems (Type ATA<return>).ECommand EchoYour modem is preset to return (or echo) commands to the hostmicroprocessor when in Command Mode.E0 No Command Echo*E1 Command EchoIIdentificationThe I command returns various modem information settings.I0= String up to 16 characters stored in non-volatile memoryI1 Product Code (MHX-920)I2 Issue ROM Check (OK or ERROR)I3 Product Identification (Firmware Version)I4 Firmware DateI5 Firmware CopyrightI6 Firmware TimeI7 Serial NumberOOn-line ModeThe O command puts the modem into data mode. This command is identicalto the A command.QQuiet ModeYour modem is preset to send responses when it executes commands, andthere after to keep the host informed of its status.*Q0 Enable modem responsesQ1 Disable modem responsesVResult Codes displayYour modem can either display result codes as words or numbers.V0 Display Result Codes as numbers*V1 Display Result Codes as words
18 MHX-920 Operating Manual: Chapter 4 ConfigurationRefer to Appendix A (page19) for a summary of themodem commands&F1 &F2Master Slave&F1 &F4&F3Master Repeater SlaveWConnection ResultThis parameter determines the modem response at the transition from DataMode to Command Mode*W0 Reports computer (DTE) baud rate as CONNECT xxxxW1 Reports wireless rate between modems as CARRIER xxxx.W2 Reports modem (DCE) baud rate as CONNECT xxxxZReset and load stored configurationThe 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 hostmicroprocessor. This command determines when the DCD is active.&C0 DCD is always ON*&C1 DCD on when modems are synchronized. DCD is alwayson when unit is configured as Master.&C2 DCD used for output data framing and Modbus mode. Seepage 33 for details.&D DTR (Data Terminal Ready)The &D command controls what action the modem performs when the DTRinput line is toggled. The DTR input is controlled by the hostmicroprocessor.*&D0 DTR line is ignored&D1 Not Supported&D2 DTR disconnects and switches to Command Mode&D3 DTR disconnects and resets modem. Modem will remainin this state until DTR again goes active.&F Load Factory Default ConfigurationThe &F command resets the modem and loads the default factoryconfiguration.&F1 Master Point-to-Multipoint. Designed to communicatewith modems configured as &F2 or &F3.&F2 Slave. Designed to communicate with another modemconfigured as &F1.&F3 Repeater. Designed to communicate with modemsconfigured as &F1 and &F4.&F4 Slave working with factory default Repeater and factorydefault Master. Communicates directly with Repeaterconfigured as &F3.&K HandshakingThe &K command controls the handshaking between the modem and hostmicroprocessor.&K0 Disable handshaking&K2 RTS/CTS input data framing. See page 33 for details.*&K3 Enable hardware handshaking (RTS/CTS)
MHX-920 Operating Manual: Chapter 4 Configuration 19Configuration options arenot stored in non-volatilememory until the WRITEcommand (&W) is executed&S DSR (Data Set Ready)The &S command controls the DSR line for the modem, and determineswhen 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 repeatersoutput the state of the master’s DTR on their local DSR line. Masteroutputs the state of a slave’s DTR on its local DSR line only inpoint-to-point mode (i.e., DTR is a two-way signal transfer in point-to-point mode, and a one-way signal transfer in point-to-multipointmode).&V View ConfigurationThe &V command displays all S registers and their current values.&E Framing Error CheckThis command enables or disables Framing Error Check. When enabled, themodem 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 dataformat (number of data bits, parity type, and number of stop bits) is definedby S register 110.*&E0 Disable Framing Error Check&E1 Enable Framing Error Check&W Write Configuration to MemoryThe &W command stores the active configuration into the modem’s non-volatile memory.Sxxx? Read S register valueThis command causes the modem to display the current setting of S registerxxx.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.
20 MHX-920 Operating Manual: Chapter 4 ConfigurationAT Command Result CodesThe MHX-920 module can display the results of a command as either textstrings or numerical data. The following chart shows resulting text string andcorresponding numeric result.0OK3NO CARRIER4ERROR7CONNECT 24008CONNECT 36009CONNECT 480010 CONNECT 720012 CONNECT 960013 CONNECT 1440014 CONNECT 1920015 CONNECT 2880017 CONNECT 3840018 CONNECT 5760033 CONNECT 11520062 CARRIER 4500064 CARRIER 20000
MHX-920 Operating Manual: Chapter 4 Configuration 21Refer to Appendix A (page45) for a summary of theS-Registers.S Registers 2 through 5cannot be stored to non-volatile memory.4.3 S RegistersThe S Registers described in this section affect the operating characteristicsof the modem.S Register 0 - Auto AnswerIf this register is set to zero, the modem will power up in command mode. Ifthis register is set to one, the modem will power up in data mode.S Register 2 - Escape CodeThis 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 fromreturning to the Command Mode. This register cannot be stored to non-volatile memory. If the modem is reset, or powered down, the default valueis restored.Default is ‘+’ (decimal 43).S Register 3 - CR Control CodeThis 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 thecharacter that appears after the modem sends a response. This register cannotbe 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 CodeRegister S4 sets the ASCII value of the linefeed character.The modem sends the linefeed character after sending a carriage returncharacter when sending text responses. This register cannot be stored to non-volatile memory. If the modem is reset, or powered down, the default valueis restored.Default is ‘LF’ (decimal 10).S Register 5 - Backspace Control CodeRegister S5 sets the ASCII value of the backspace character.This character is both the character created by entering BACKSPACE andthe character echoed to move the cursor to the left. This register cannot bestored to non-volatile memory. If the modem is reset, or powered down, thedefault value is restored.Default is ‘BS’ (decimal 8).
22 MHX-920 Operating Manual: Chapter 4 ConfigurationOnly one Master can existfor each network.S Register 101 - Operating ModeThe Operating Mode (register S101) partly defines the “personality” of theMHX-920 module. Allowable settings for this register are 1 through 5 asfollows:.• S101=1 Master Point to Multipoint• S101=2 Master Point to Point• S101=3 Slave• S101=4 Repeater• S101=5 Master - Diagnostics (see Section 4.4)The default for this register depends on which factory default is selected asshown 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, thereis always only one Master. All other units should be configured as eitherSlaves or Repeaters. When defined as a Point-to-Multipoint Master, themodem broadcasts data to all Slaves and Repeaters in the network, and isalso the ultimate destination for data transmitted by all Slaves andRepeaters. In addition, the Master defines the following network parametersto be utilized by all other modems in the network (See the appropriatesections for a complete description of these parameters):nMaximum Packet Size (S112)nMinimum Packet Size (S111)nWireless Link Rate (S103)nHop Interval (S109)2)Master - Point to Point. This mode of operation is identicalto Master Point-to-Multipoint, with the exception that the Master onlybroadcasts to one particular Slave or Repeater. The modem with whichcommunication occurs is defined by the Unit Address (S105). For example,if a Slave has been assigned Unit Address 100, and the Master wishes tocommunicate with that Slave, the Master must also be assigned a UnitAddress of 100. If there are Repeaters in the network, they will pass thepacket through to the Slave, and vice versa. Because Repeaters also haveSlave functionality (i.e., a Repeater can be connected to a terminal), theMaster can choose to communicate solely with a Repeater. This would beaccomplished by assigning the same Unit Address to both the Master andthe Repeater.
MHX-920 Operating Manual: Chapter 4 Configuration 23PHP=1 PHP=2PHP=1SHP=2MasterRepeaterSlaveNetwork 50Hop Pattern 1Hop Pattern 2Figure 7 - RepeaterOperationMaster RepeaterSlaveRepeaterSlavePHP=1 PHP=1SHP=2PHP=2PHP=2SHP=3 PHP=3Hop-Pattern 1Hop Pattern 2Hop Pattern 3Figure 8 - A NetworkUtilizing Three HoppingPatternsIf there is no DTE connectedto the Repeater, turn offhandshaking (&K0) and setthe baud rate to 115K.3)Slave. Up to 65535 Slaves may exist in a network, all of whichcommunicate with the common Master (either directly or via Repeater(s)).Slaves cannot directly communicate with other. Slaves only provideacknowledgement for packets of data sent by the Master when the Master isin Point-to-Point mode. In multipoint mode, multiple slaves would conflictwith one another if they were all trying to acknowledge the Master at thesame time. The Master does, however, send acknowledgements to allmessages it receives from Slaves. The Master initiates communications bysending a broadcast message to all Slaves. All Slaves are free to respond ina “Slotted ALOHA” fashion, meaning that each Slave can choose one ofseveral windows in which to transmit. If there happens to be two Slavesattempting to talk at the same time, the Master may not receive the data, andthe Slaves therefore would not get an acknowledgement. At this point, theSlaves would attempt to get the information through at random timeintervals, thus attempting to avoid any more conflicts. Special parameterswhich control the Slave’s response characteristics can be modified with SRegisters S115 and S213.4) Repeater. A more precise title would be Repeater/Slave, because aRepeater also has much of the same functionality as a Slave. A terminal canbe connected at the Repeater location and communicate with the Masterterminal. There is no restriction to the number of Repeaters in a network,allowing for communication over virtually limitless distances. The presenceof one Repeater in a network automatically degrades system throughput byhalf. Additional Repeaters, regardless of the quantity, do not diminishsystem throughput any further. To understand Repeater operation, considerthe module as belonging to two hopping patterns at the same time: ThePrimary Hopping Pattern and the Secondary Hopping Pattern. In Figure 7,the Master belongs to Hopping Pattern 1, and communicates with theRepeater on this hopping pattern. The Slave belongs to Hopping Pattern 2,and communicates with the Repeater on this hopping pattern. The wholesystem belongs to Network 50 (i.e., all units must be assigned the sameNetwork Address (S104), which in this case was selected to be 50. Notethat Slaves and Master only communicate on their respective PrimaryHopping Pattern. Repeaters communicate on the Primary Hopping Patternwhen communicating with the Master (or with another Repeater betweenitself and the Master). Repeaters communicate on their Secondary HoppingPattern when communicating with Slaves (or with another Repeater betweenitself and the Slaves). Figure 8 shows another example.If the Repeater is not also being used as a Slave (there is no DTE connectedto the serial port), it is recommended that the Repeater’s baud rate be set to115K, and that handshaking be disabled (&K0). This will help ensure asmooth flow of data through the network.
24 MHX-920 Operating Manual: Chapter 4 ConfigurationThe Master determines theWireless Link Rate. Thissetting on all other modemsis ignored..S Register 102 - Serial Baud RateThe Serial Baud Rate is the current speed that the modem is using tocommunicate with the DTE. In command mode, the module “autobauds,”meaning that it will adapt to the baud rate of the DTE equipment to which itis connected. Therefore, when in command mode, you may change the baudrate of your equipment, and the MHX-920 will automatically adjust to thisbaud rate once an AT string is issued. The new baud rate is stored inregister S102. If you issue a command to change the value of S102, theinstant you issue another command, the baud rate will revert back to that ofthe DTE equipment. Therefore, it is advisable to operate in Command Modeat the desired baud rate for Data Mode.See page 14 for additional information.The possible values are:1 1152002 576003 384004 288005 192006 14400*7 96008 72009 480010 360011 2400It is generally advisable to choose the highest rate that your terminalequipment will handle to maximize performance, unless a limitation on theavailable bandwidth is desired. If the DTE is a personal computer, the portcan usually be used reliably at 115200. Issuing the &Fx command (factorydefault) does not affect the current setting of S102.S Register 103 - Wireless Link RateThe Wireless Link Rate is the speed and optimization method for whichmodems will communicate over the RF link. It is only necessary to set thisparameter on the Master unit. Units configured as Repeaters and Slaves willignore this setting, and adjust automatically to the rate of the Master.The allowable settings are:*2 Fast without Forward Error Correction4Fast with Forward Error CorrectionDepending on the application requirements, each mode will providedifferent throughput and performance. Appendix E. Performance Tablesgive some indication of the performance to be expected in each mode.In general, Forward Error Correction (FEC) reduces throughput, but in someenvironments will actually increase throughput. FEC can reduce the numberof bad data packets, and hence reduce the need to retransmit.
MHX-920 Operating Manual: Chapter 4 Configuration 25Select a Network Addressand assign it to all unitswhich will be included in thenetwork.Warning: Microhard Systemsstrongly recommends changing theNetwork Address to a valuedifferent than the factory defaultbefore deploying the network.Use the same Unit Addresson both units for point-to-point mode. In multipointmode, set each Slave andRepeater to a different UnitAddress.Valid Unit Addresses are 1to 65535.S Register 104 - Network AddressThe Network Address defines the membership to which individual units canbe 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 thecommunications interchange. Valid values for the Network Address rangefrom 0 to 65535, inclusive.To enhance privacy and reliability of communications where multiplenetworks may operate concurrently in close proximity, it is suggested that anatypical value be chosen – perhaps something meaningful yet not easilyselected by chance or coincidence.Default is 1.S Register 105 - Unit AddressIn 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 UnitAddress uniquely identifies each Slave and Repeater from one another.Each unit in a multipoint system must have a unique Unit Address rangingfrom 1 to 65535. Do not use 0 as a Unit Address, and do not use a UnitAddress more than once within the same Network. This is required becausethe Master must be able to acknowledge each unit individually, based on theUnit Address.S Register 106 - Primary Hopping PatternS Register 206 - Secondary Hopping PatternSince the MHX-920 is a frequency-hopping modem, the carrier frequencychanges periodically according to one of 64 pseudo-random patterns,defined by the Primary and Secondary Hopping Patterns. Valid entries foreach are 0 through 63. Patterns 0 through 61 are pre-programmed, withdetails provided in Appendix F. Patterns 58 through 63 are user-editablepatterns. See Appendix F for details.The concept of Primary and Secondary Hopping Patterns was introduced inthe 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;
26 MHX-920 Operating Manual: Chapter 4 ConfigurationMaster SlaveMaster Repeater SlaveMaster Repeater1 Repeater2 SlaveSlaves and Masters do notuse Secondary HoppingPatternsRemember to assign aunique Unit Address (1 to65535) to each unit in thesystemthe following diagrams illustrate the methodology for deploying simple tocomplicated networks: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]It is reasonable to consider a Repeater as being both a Slave and a Master,alternating between Primary and Secondary Hopping Patterns as the unitchanges channel. Consider R1 in the illustration below. Whencommunicating with the Master, R1 is acting like a Slave on PrimaryHopping Pattern 1. When communicating with R2 and S4, R1 is acting likea Master on Secondary Hopping Pattern 2. If multiple Repeaters are used,they should have different Secondary Hopping Patterns:←→ R1[1,2] ←→ R2[2,5] ←→ S3[5]M[1] ←→ S4[2]←→ R5[1,3] ←→ R6[3,6] ←→ S7[6]←→ R8[1,4] ←→ S9[4]Note that all units have a unique Unit Address.Networks of any complexity can be created by linking multiple Repeatersand Slaves:←→ R1[1,2] ←→ S2[2]←→ S3[2]←→ ←→ R5[3,6] ←→ S6[6]M[1] R4[1,3] ←→ S7[6]←→ R8[3,7] ←→ R9[7,8] ←→ S10[8]←→ S11[1]←→ S12[1]With a limitation of 64 hopping patterns, one might suspect that there is alimitation to the number of repeaters in a system. However, if the units arefar enough away from one another, hopping patterns may be reused indifferent sections of the network, without causing interference.
MHX-920 Operating Manual: Chapter 4 Configuration 27All units within a networkmust use the sameencryption key.Warning: Microhard Systemsstrongly recommends changing theEncryption Key to a valuedifferent than the factory defaultbefore deploying the network.S Register 107 - Encryption KeyThe Encryption Key provides a measure of security and privacy ofcommunications by rendering the transmitted data useless without thecorrect key on the receiver. Valid Encryption Keys range from 0 to 65535.Keep in mind that all units within the network must use the same key forcommunications to succeed.S Register 108 - Output Power LevelThe Output Power Level determines at what power the MHX-920 transmits.The MHX-920’s sensitive receiver can operate with very low power levels,so it is recommended that the lowest power necessary is used; usingexcessive power contributes to unnecessary “RF pollution”.The allowable settings are:01 mW110 mW*2 100 mW31000 mWIdeally, you should test the communications performance between unitsstarting from a low power level and working upward until the RSSI issufficiently high and a reliable link is established. Although the conditionswill vary widely between applications, typical uses for some of the settingsare described below:Power Use1 mW For in-building use, typically provides a link up to 300 feet on thesame floor or up/down a level. Outdoors, distances of 10 km can beachieved if high-gain (directional) antennas are placed high aboveground 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(1 W)Typically provides communications up to a distance of 1000 feet ormore in-building on the same floor or up/down a few levels,depending on building construction (wood, concrete, steel, etc.). Inideal line-of-sight conditions, up to 30 km* or more can beachieved. Note that only an antenna with a gain of no more than 6dBi may be used. Any higher is a violation of FCC rules. SeeIMPORTANT warning below.* These outdoor distances assume antennas are mounted at least 100 ftabove ground level
28 MHX-920 Operating Manual: Chapter 4 ConfigurationThe hopping interval iscontrolled by the master.The slave and repeater unitswill use the hopping intervalsetting from the master.Warning: Communication willfail if the hopping interval is notset according to the guidelines ofAppendix E.;..IMPORTANT:FCC Regulations allow up to 36 dBi effective radiated power (ERP).Therefore, the sum of the transmitted power (in dBm), the cabling lossand the antenna gain cannot exceed 36 dBi.1 mW = 0 dBm10 mW = 10 dBm100 mW = 20 dBm1000 mW = 30 dBmFor example, when transmitting 1 Watt (30 dBm), the antenna gaincannot exceed 36 - 30 = 6 dBi. If an antenna with a gain higher than 6dBi were to be used, the power setting must be adjusted appropriately.Microhard Systems Inc. limits the MHX-920’s transmitted power to100mW for all units purchased with antennas with gain above 6dBi.S Register 109 - Hopping IntervalThis option determines the frequency at which the modems change channel.Note that the Master controls this parameter for the entire network. Thissetting is ignored in units configured as Slaves or Repeaters.The allowable settings are:18 msec212 msec316 msec*4 20 msec530 msec645 msec780 msec8120 msecSome 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 packetsize and link rate.
MHX-920 Operating Manual: Chapter 4 Configuration 29When S114=0, theMinimum and MaximumPacket Size is controlled bythe Master , therefore, theSlave and Repeater units willuse the Minimum andMaximum Packet Sizesetting from the Master.When S114=1, Slave andRepeater units will use theirlocal S111 and S112 settingsfor packet size control inpoint-to-point modeS Register 110 - Data FormatThis register determines the format of the data on the serial port. Allowablesettings are:*1 8 bits, No Parity, 1 Stop28 bits, No Parity, 2 Stop38 bits, Even Parity, 1 Stop48 bits, Odd Parity, 1 Stop57 bits, No Parity, 1 Stop67 bits, No Parity, 2 Stop77 bits, Even Parity, 1 Stop87 bits, Odd Parity, 1 Stop97 bits, Even Parity, 2 Stop10 7 bits, Odd Parity, 2 Stop11 9 bits, No Parity, 1 StopS Register 111 - Packet Minimum SizeS Register 112 - Packet Maximum SizeS Register 114 - Packet Size ControlS Register 116 - Packet Character TimeoutThese settings determine the conditions under which the modem willtransmit accumulated data over the air.S Register 111 - Minimum SizeValid entries for this register are 1 to 255 bytes, which defines the minimumnumber of bytes to receive from the DTE before encapsulating them in apacket and transmitting over the air.Note that if register S114=0 at any particular Repeater or Slave, thatRepeater or Slave will ignore its own S111 register and abide by theMaster’s S111 setting. If S114=1 at any particular Repeater or Slave, thatRepeater or Slave will use its own local S111 setting. The default for S111is 1 byte.S Register 112 - Maximum SizeThis setting has a range of 2 to 255, and defines the maximum number ofbytes from the DTE which should be encapsulated in a packet. This valueshould be greater than the minimum packet size, but not smaller than isnecessary for reliable communications. If the wireless link is consistentlygood 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) anddata is frequently retransmitted, the maximum packet size should bereduced. This decreases the probability of errors within packets, andreduces the amount of traffic in the event that retransmissions are required.Note that if register S114=0 at any particular Repeater or Slave, thatRepeater or Slave will ignore its own S112 register and abide by theMaster’s S112 setting. If S114=1 at any particular Repeater or Slave, thatRepeater or Slave will use its own local S112 setting. The default for S112is 255 bytes.
30 MHX-920 Operating Manual: Chapter 4 ConfigurationS Register 114 - Packet Size ControlThis register, when set to 1, allows for Repeater and Slaves’ local S111 andS112 to override those of the Master when the system is operating in point-to-point mode. This may be useful for controlled asymmetrical data flow.The master always transmits in the first portion of the hop interval, withslaves and repeaters responding back to the master on the second portion ofthe hop interval. Setting the master’s max packet size smaller than that ofthe slave would ensure that the master uses less of the available time withinthe hop interval for transmitting data, thereby allocating more time for theslave.S Register 116 - Packet Character TimeoutThis register has valid entries of 0 to 254 milliseconds. The PacketCharacter Timeout timer looks for gaps in the data being received from theDTE. The timer is only activated after the Minimum Packet Size has beenaccumulated in the modem. After which, if the timer detects a gap in thedata exceeding the Packet Character Timeout value, the modem willtransmit the data.The MHX-920 will accumulate data in its buffers from the DTE until one ofthe 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 PacketCharacter Timeout interval has elapsed.The default for the Packet Character Timeout is 8 ms. If set to 0 ms, theunit will buffer exactly the minimum packet size before transmitting.S Register 113 - Packet RetransmissionsThis register applies to both Master and Repeater operation. It does notapply to Slave operation. In point-to-multipoint mode, the Master willretransmit each data packet exactly the number of times defined by thePacket Retransmissions parameter. In point-to-point mode, the Master willonly retransmit the packet if it does not get an acknowledgement from theslave with which it is communicating. In this case, the Master will continueto retransmit until an acknowledgement is received, or the retransmissionlimit is reached. When the retransmission limit is reached, the Masterdiscards the packet. The Master retransmits once at the beginning of eachhopping interval until the limit is reached. This parameter is not necessaryin Slave units since all Slaves receive acknowledgement from the Master,and needn’t blindly retransmit if it has knowledge that the Master hasreceived the packet.. As discussed previously, the Repeater effectivelybehaves as both a Master and a Slave. When the Repeater is tuned to itsSecondary Hopping Pattern (acting as a Master), the Packet RetransmissionsParameter comes into play. The Repeater will re-send packets of data on toSlaves or other Repeaters exactly the number of times defined by the PacketRetransmissions parameter.Recipients of the packet will discard any duplicates The valid settings forthis parameter are 0 to 255 retransmissions. The default is 1.
MHX-920 Operating Manual: Chapter 4 Configuration 31S Register 213 - Packet Retry LimitPacket Retry Limit is analogous to Packet Retransmissions, but specificallyapplies to Slaves and Repeaters. This parameter is not used by the Master.Because the Slave has the advantage of receiving acknowledgements fromthe Master, it is not necessary to blindly retransmit each packet. If the Slavedoes not get an acknowledgement on the next hop, it will retransmit itspacket. This will continue until the Packet Retry Limit is reached or anacknowledgement is received. If the limit is reached, the modem will giveup and discard the data. Valid settings are 0 to 255 retries. The defaultvalue is 2.The Repeater makes use of this parameter when it is tuned to its PrimaryHopping Pattern and is acting like a Slave.S Register 115 - Packet Repeat IntervalA parameter that is specific to Slaves and Repeaters is the Packet RepeatInterval.The allowable settings are 1 through 255. The default is 1.This parameter defines a range of random numbers that the Slave will use asthe next slot in which it will attempt to send the packet. For example, if thisregister is set to 7, the Slave will choose a number between one and seven asthe next slot in which to transmit. Suppose the random number generatorpicks 5, then the Slave will transmit in the fifth time slot. A Slave willtransmit a maximum of once per hopping interval, however, depending onthe duration of the hopping interval and the maximum packet size, morethan one slot per hop is potentially available. The Slave will transmit morefrequently when a Repeat Interval with a smaller range is selected. Choose1 to have the Slave transmit in the first available slot. Choose higherintervals for less frequent transmission, or to avoid collisions between manySlaves in the system.This register is always disregarded and taken as S115=1 in Point-to-Pointmode.
32 MHX-920 Operating Manual: Chapter 4 ConfigurationS Register 117 - Modbus ModeModbus Mode allows for the MHX-920 to be fully Modbus compatible. ForModbus operation, the general requirement is to get the packet of data to thereceiving serial port with no gaps in the data. The MHX-920 incorporates a“Modbus Mode” which implements a delay at the receiving modem toensure that no gaps are introduced. For most applications, the followingsettings are suitable for Modbus operation:1. Set Modbus Mode parameter S117 = 12. Set the minimum packet size (S111) to 1 byte3. Set the character timeout S116 (rounded to the nearest ms) to roughly2.5 byte lengths. For example, at 9600 baud, S116 = 1/9600 x 10 x 2.5 x 1000 = 2.6msRounded up, S116 = 3ms4. 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 = 2ms5. Set S120 as follows:Slave SideS120 = (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 msMaster SideS120 = (Hop Interval in ms) x (1 + # of Repeaters over 1)6. Try to set the hop interval as short as possible while still ensuringadequate throughput. It is recommended to set the Hop Interval andMaximum Packet Size as specified in Appendix E. PerformanceTables. For example, for Master to Slave communication with no FEC,If a throughput of 60kbps is required, set the Hop Interval S109=3, andset the Maximum Packet Size S112=110.The allowable settings for this register are:*0 Disabled1Enabled
MHX-920 Operating Manual: Chapter 4 Configuration 33S Register 118 - RoamingThis mode is activated on slaves and repeaters by setting register S118=1.In this mode, a slave/repeater looks for synchronization with a Masterhaving the same network address and encryption key, but without regard forthe hopping pattern S106. Once the slave/repeater finds such a master, ittunes to that master’s hopping pattern. If synchronization is lost, theslave/repeater will again begin searching for a new master. Using thisalgorithm, a mobile unit can ‘roam’ and automatically synchronize with anew master once it loses communication with the previous one. It isessential that all Masters with which a roaming slave/repeater will becommunicating with use a hopping pattern from within the same group. SeeAppendix F. The allowable settings for this register are:*0 Disabled1EnabledS Register 119 - Quick Enter to CommandBy setting this register to 1, a delay of 5 seconds is introduced at power-upbefore the modem goes into data mode. If, during these 5 seconds, the userenters ‘mhx’ the modem will instead go into Command Mode, and replywith ‘OK’. The terminal baud rate must be set to 9600 baud. If an incorrectcharacter is entered, the modem will immediately go into Data Mode. Thedefault setting is 1 - Enabled.S Register 120 - RTS/DCD FramingS Register 121 - DCD TimeoutThe MHX-920 supports two special types of data framing:• Input (or RTS/CTS) Data Framing; and,• Output (or DCD) Data FramingInput Data Framing is enabled by configuring the Handshaking Parameter as&K2. This type of framing makes use of the S120 parameter as illustratedin Figure 9. Parameter S120 can be set to any value between 0 and 254 ms.RTSCTSTXDS120 (ms)Data going into MHX-9100 to 1 msFigure 9 - Input Data Framing
34 MHX-920 Operating Manual: Chapter 4 ConfigurationTo enable output (DCD) data framing, set the Data Carrier Detect parameteras &C2. This type of framing uses both S120 and S121 registers as shownin Figure 10. Valid ranges for each parameter are 0 to 254 msDCDRXD Data leaving MHX-910S120 (ms) S121 (ms)Figure 10 - Output Data FramingS Register 122 - Remote ControlThis register either disables or enables remote control at a repeater or slaveunit. When disabled, a slave/repeater’s settings may be remotely read by themaster, but may not be remotely modified. When enabled, theslave/repeater allows the network master full remote control access. SeeSection 4.4.3 for details. The default is 0 - disabled.S Register 123 - RSSI ReadingThis register displays the average signal strength in dBm over the previousfour hop intervals. The value in this register is also reflected in status linesRSSI1,2 and 3. See Section 2.2 for a description of RSSI, and how it isderived.
MHX-920 Operating Manual: Chapter 4 Configuration 354.4 Diagnostics, Statistics and Remote ControlThe MHX-920 provides several commands which are very useful fortroubleshooting and analyzing the performance of the radio system.4.4.1 Spectrum Analyzer Feature (ATG)Issuing the command ATG <return>,causes the MHX-920 to perform asweep of the entire operating spectrum, giving a signal strength read-out indBm for each channel as shown below:Noise level, '*'- mean value, '.'- max valuech 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 200kHz increments. This feature also displays average received signal strengthfor 12 channels above the 902-928 MHz ISM band. This area of thespectrum is used by paging networks.When deploying a network, the spectrum analyzer feature is useful fordetermining which parts of the ISM band may be noisy. This knowledgecan be used to select an appropriate hopping pattern, or for creating acustom hopping pattern which avoids those frequencies.In addition, the presence of extremely high paging noise (> -25dBm) mayindicate a need to install Microhard’s external cavity filter in line with theantenna. See Chapter 5 for details.4.4.2 Statistics (ATP)The ATP <return> command provides a list of several statistics as follows:# of data packets sent = 0# of data packets received = 0# of Slave's retries = 0# of Slave's packets dropped = 0# of Slave's sync errors = 0# of CRC errors = 0OKThe MHX-920 starts the statistics count at zero each time the unit ispowered up, or after the ATP command has been issued. By entering theATP command, all statistics are cleared back to zero. The maximum limitfor each statistic is 65535.
36 MHX-920 Operating Manual: Chapter 4 Configuration4.4.3 Remote Control and Diagnostics (S101=5)This is a very powerful tool which allows user to remotely configure andinterrogate all units in a multipoint system from the Master unit. Simply byhaving 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 theslave/repeater of interest, set S101=5, go online, and interrogate/modifyvirtually all parameters of the remote repeater/slave unit. It should be notedthat when the master goes online, all other units belonging to the networkwill synchronize with the master, but only the unit whose unit addressmatches the master’s will respond to the master’s diagnostic commands.In addition, in diagnostics mode, the master can change its unit address ‘on-the-fly,’ avoiding the delays of going into command mode, modifying theunit address, going back online and re-synchronizing with the entirenetwork, before interrogating a new slave/repeater. The master’s unitaddress can be changed while still maintaining synchronization with theentire network, allowing for quick and efficient diagnostic sessions with allremote units. Ensure that register S122=1 on any slave/repeater that youwish to remotely modify.Table 4 provides a diagnostics command summary. The first column is alist of commands that may be issued at the master. The second column isthe corresponding remote register. In general, any command issued withoutany additional parameters is a read command. For example, if you type:0 <return>The remote slave/repeater will send back the value if its S101 register. Onthe Master terminal screen, you would see:0 (this is the 0 that you typed, echoed back locally)3 (this indicates that the remote’s S101=3)If you type:04 <return>This command would change the remote’s operating mode to S101=4(repeater). The remote unit should return ‘OK’. Remember, if the remote’sS122=0 (remote control disabled), the remote will respond with ‘ERROR’.In Table 4, Column 1, the meanings of the format is as follows:COMMAND A command without (x) indicates that you may not add anyadditional parameters. i.e., you may only read back the valueof 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 aparameter. Issuing this command without a parameter readsthe corresponding remote’s register. Issuing this commandwith the additional parameter ‘x’ changes the correspondingremote’s register to ‘x’. Remember, any changes you wish toretain in the event of a powerdown or reset should be stored tonon-volatile memory by issuing the write command ‘e’.
MHX-920 Operating Manual: Chapter 4 Configuration 37Table 4 - Remote Control and DiagnosticsCommand Remote Register Description0(x) S101 Operating Mode1(x) S102 Baud Rate2(x) S108 Output Power3(x) S110 Data Format4(x) S115 Repeat Interval5(x) S116 Character Timeout6(x) S120 RTS/DCD Framing7(x) S121 DCD Timeout8(x) S117 Modbus Mode9(x) S213 Retry Limitatest string Read back 'OK' from remotea1 test string Read back 'Microhard Systems, Inc.' fromremotea2 test string Read back 64 character test string fromremotea3 test string Read back 255 character test string fromremoteb(x) &E Framingc(x) &C DCDd(x) &K Handshakinge&W WritefS123 RSSIg(x) S104 Network Addressh(x) S106 Hopping PatternI(x) S206 Secondary Hopping Patternj(x) S113 Retransmissionsk1 statistics Read # of data packets sentk2 statistics Read # of data packets receivedk3 statistics Read # of Slave's retriesk4 statistics Read # of Slave's packets droppedk5 statistics Read # of Slave's sync errorsk6 statistics Read # of CRC errorsk255 statistics Clear statisticsl(x) S119 Quick Enter to Command Modem(x) S118 Roamingn(x) S114 Packet Size Controlo(x) S111 Min Packet Sizep(x) S112 Max Packet Size
38 MHX-920 Operating Manual: Chapter 4 ConfigurationAs mentioned previously in this section, there are some settings that can bechanged to the master’s own registers while in diagnostics mode. The mostuseful is the unit address. By changing the master’s unit address to that ofanother slave in the network while in diagnostics mode, users can quicklyinterrogate/modify many different slave’s settings without the delaysassociated with switching between command and data modes. Thecommands which apply to the master’s own registers are shown in Table 5.Table 5 - Master Diagnostics CommandsCommand Master Register Descriptionr(x) S105 Unit AddresssS101 back to normal operating modet(x) S109 Hopping Intervalu(x) S104 Network Addressv(x) S106 Hopping Pattern
MHX-920 Operating Manual: Chapter 5 Installation 395. InstallationThe installation, removalor maintenance of allantenna components mustbe carried out byqualified and experiencedpersonnel.The installation, removal or maintenance of all antennacomponents must be carried out by qualified andexperienced personel.The MHX-920 complies with FCC part 15 at the modular level foroperation in the license-free 902-928 MHz ISM band. This chapterprovides guidelines for installing and deploying equipment whichincorporates the MHX-920 module.5.1 Estimating the Gain MarginSuccessful communication between MHX-920 modules is dependent onthree main factors:• System Gain• Path Loss• InterferenceSystem gain is a calculation in dB describing the performance to beexpected between a transmitter-receiver pair. The number can be calculatedbased on knowledge of the equipment being deployed. The following fourfactors 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 betweenthe transmitting antenna and the MHX-920 module)3. Receiver gain (Receiving antenna gain minus cabling loss between thereceiving antenna and the module)4. Receiver sensitivity (Specified as -105 dBm on the MHX-920 module)In the following illustration, the transmitting antenna has a gain of 6 dB, andthe receiving antenna has a gain of 3 dB. The cable loss between themodule and the antenna is 2 dB on both the transmitting and receiving side.Transmitter30 dBmOutput PowerReceiverSensitivity =-105 dBmCable Loss = 2 dBCable Loss = 2 dBAntenna Gain = 6 dB Antenna Gain = 3 dBThe power level has been set to 30 dBm (1W) on the transmitter, and thereceiver sensitivity for the MHX-920 is -105 dBm.System gain would be calculated to be:30 - 2 + 6 + 3 - 2 + 105 = 140 dB.
40 MHX-920 Operating Manual: Chapter 5 InstallationBase Height (m)MobileHeight(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) betweenequipment 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 ensurereliable communication. Gain margin is the difference between system gainand path loss. Referring to the same example, suppose the path loss is 100dB, the gain margin would be 40 dB, which is more than adequate forreliable communication.Path loss is a very complicated calculation which mainly depends on theterrain profile, and the height of the antennas off the ground.The following table provides path loss numbers for varying antenna heightsand antenna separation: These numbers are real averages taken from ruralenvironments. They do not apply to urban, non-line-of-sight environments.Distance(km)Base Height(m)Mobile Height(m)Path Loss(dB)5 15 2.5 116.55 30 2.5 110.98 15 2.5 124.18 15 5 117.78 15 10 10516 15 2.5 135.316 15 5 128.916 15 10 116.216 30 10 109.616 30 5 122.416 30 2.5 128.8Once the equipment is deployed, you can verify the signal strength byentering into Command Mode and reading Register S123. This registerprovides the average signal strength in dBm. The minimum strength forcommunication is roughly -105 dBm. For consistent reliablecommunication, you should try to deploy the equipment such that signalstrength exceeds -95 dBm.
MHX-920 Operating Manual: Chapter 5 Installation 415.2 Antennas and CablingThis section describes the recommended procedure for installing cablingand antennas for use with the MHX-920 module.5.2.1 Internal CablingThe most common method for installing the module is to run a cable fromthe module’s MCX connector to a reverse TNC bulkhead connector on thechassis of the equipment as shown in Figure 11. This cable can bepurchased from Microhard Systems.RG316 Cable with MCX maleconnectorand Reverse TNCbulkheadconnector Reverse TNC ConnectorMCX female connectorMHX-910Figure 11. Suggested Internal CablingCable 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 ReverseTNC connections.
42 MHX-920 Operating Manual: Chapter 5 InstallationThe installation, removal ormaintenance of all antennacomponents must be carried outby qualified and experiencedpersonnel.Never work on an antenna systemwhen there is lightning in thearea.Direct human contact with theantenna is potentially unhealthywhen the MHX-920 is generatingRF energy. Always ensure thatthe MHX-920 equipment ispowered down during installation.5.2.2 Installing External Cables, Antennas and LightningArrestorsThe installation, removal or maintenance of all antenna components must becarried 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 theMHX-920 is generating RF energy. Always ensure that the MHX-920equipment is powered down during installation.Surge ArrestorsThe most effective protection against lightning is to install two lightning(surge) arrestors. One at the antenna, and the other at the interface with theequipment. The surge arrestor grounding system should be fullyinterconnected with the transmission tower and power grounding systems toform a single, fully integrated ground circuit. Typically, both ports on surgearrestors are N-female.CablingThe following coax cables are recommended:Cable Loss (dB/100ft)LMR 195 10.7LMR 400 3.9LMR 600 2.5Factors to take into consideration when choosing a cable are:• price;• bend radius limitations (the lower performance cables generally canbend more sharply)• performance requirements; and,• distance between the equipment and the antenna.When installing the cable, always begin fastening at the top near the antennaconnector/surge arrestor. The cable must be supported at the top with ahose 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. Ifproperly grounded surge arrestors are not installed at both the top and thebottom of the cable, then the cable should be grounded to the tower at theselocations using a cable grounding kit. If the tower is non-conductive, then aseparate conductor, physically separate from the cable, should be run downthe tower.
MHX-920 Operating Manual: Chapter 5 Installation 43To comply with FCC regulations,.you must limit ERP to 36 dBm orless.AntennaBefore choosing an antenna, you should have some knowledge of the pathloss and the topology of the equipment. If the equipment is in a fixedlocation and is to communicate with only one other unit also in a fixedlocation, then a Yagi antenna is suitable. Choose a Yagi with enough gainto ensure adequate gain margin. When deploying the Yagi, point theantenna towards the intended target, ensuring the antenna elements areperpendicular 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 fromthe antenna cannot exceed +36 dBm ERP.With the MHX-920 set to full power, ERP is calculated as follows: ERP = 30 - (Cabling and Connector Losses) + (Antenna Gain) < 36Use the guidelines in the previous section for calculating cable andconnector losses. If cabling and connector losses are 2 dB, then themaximum allowable gain of the antenna will be 8 dB.External FilterAlthough the MHX-920 is capable of filtering out RF noise in mostenvironments, there are circumstances that require external filtering. Pagingtowers, and cellular base stations in close proximity to the MHX-920antenna can desensitize the receiver. Microhard Systems’ external cavityfilter eliminates this problem. The filter has two N-female ports and shouldbe connected in line at the interface to the RF equipment.WeatherproofingType N and RTNC connectors are not weatherproof. All connectors shouldbe taped with rubber splicing tape (weatherproofing tape), and then coatedwith a sealant.
44 MHX-920 Operating Manual: Chapter 5 Installation
MHX-920 Operating Manual: Appendix A Modem Command Summary 45A. Modem Command SummaryThe following provides a command summary for the MHX-920 module. Factory settings are denoted with a ‘*’.AT CommandsAAnswerECommand EchoE0 No Echo* E1 Command EchoIIdentificationI0 CustomI1 Product CodeI2 ROM Checksum testI3 Firmware VersionI4 Firmware DateI5 CopyrightI6 Firmware TimeI7 Serial NumberOOn-line ModeQQuiet Mode* Q0 Enables Result CodesQ1 Disables Result CodesVResult Codes DisplayV0 Display as Numbers* V1 Display as WordsWConnection Result* W0 Reports DTE as CONNECT xxxxW1 DTE) rate as CARRIER xxxx.W2 Reports DCE as CONNECT xxxxZReset 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 memorySxx? Read S register valueSxx=yy Set S register valueResult Codes0OK 12 CONNECT 96003NO CARRIER 13 CONNECT 144004ERROR 14 CONNECT 192007CONNECT 2400 15 CONNECT 288008CONNECT 3600 17 CONNECT 384009CONNECT 4800 18 CONNECT 5760010 CONNECT 7200 33 CONNECT 11520064 CARRIER 20000 62 CARRIER 45000S RegistersS0 Auto Answer0 = power up in Command Mode,*1 = power up in Data ModeS2 Escape code [0...255] default ‘+’ (43)S3 CR character [0...255] default <cr> (13)S4 Line Feed [0...255] default <lf> (10)S5 Backspace [0...255] default <bs> (8)S101 Operating Mode1 - Master Point to Multipoint2 - Master Point to Point3 - Slave4 - Repeater5 - Master DiagnosticsS102 Serial Baud Rate1 = 115200, 2 = 57600, 3 = 384004 = 28800, 5 = 19200, 6 = 14400*7 = 9600, 8 = 7200, 9 = 4800,10 = 3600, 11 = 2400S103 Wireless Link Rate*2 = Fast w/o FEC4 = Fast with FECS104 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 Level0 = 1 mW, 1 = 10 mW, *2 = 100 mW, 3 = 1000 mWS109 Hopping Interval1 = 8 msec, 2 = 12 msec, 3 = 16 msec,*4 = 20 msec, 5 = 30 msec, 6 = 45 msec,7 = 80 msec, 8 = 120 msecS110 Data Format* 1 = 8N1, 2 = 8N2, 3 = 8E1, 4 = 8O15 = 7N1, 6 = 7N2, 7 = 7E1, 8 = 7O19 = 7E2, 10 = 7O2, 11 = 9N1S111 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=EnabledS115 Packet Repeat Interval [1..255]Default = 1S116 Packet Character Timeout [0...254 ms]S117 Modbus Mode*0 = Disabled, 1 = EnabledS118 Roaming*0 = Disabled, 1 = EnabledS119 Quick Enter to Command0 = Disabled, *1 = EnabledS120 RTS/DCD Framing Interval [0...254 ms]S121 DCD Timeout [0...254 ms]S122 Remote Control*0 = Disabled, 1 = EnabledS123 RSSI (dBm)
46 MHX-920 Operating Manual: Appendix A Modem Command Summary
MHX-920 Operating Manual: Appendix B Serial Interface 47B. Serial InterfaceModem(DCE)SignalHostMicroprocessor(DTE)1 DCD →IN2 RX →IN3← TX  OUT4← DTR  OUT5 SG →IN6 DSR →IN7← RTS  OUT8 CTS →INArrows denote the direction thatsignals are asserted (e.g., DCDoriginates at the DCE and tells theDTE that a carrier is present).The MHX-920 module uses 8 pins on the header connector for asynchronousserial I/O. The interface conforms to standard RS-232 signals without levelshifting, 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 withanother MHX-920.RX Receive Data - Output from Modem - Signals transferred from the MHX-920 are received by the DTE via RX.TX Transmit Data - Input to Modem - Signals are transmitted from the DTE viaTX to the MHX-920.DTR Data Terminal Ready - Input to Modem - Asserted (TTL low) by the DTE toinform the modem that it is alive and ready for communications.SG Signal Ground - Provides a ground reference for all signals transmitted byboth DTE and DCE.DSR Data Set Ready - Output from Modem - Asserted (TTL low) by the DCE toinform the DTE that it is alive and ready for communications. DSR is themodem’s equivalent of the DTR signal.RTS Request to Send - Input to Modem - A “handshaking” signal which isasserted by the DTE (TTL low) when it is ready. When hardwarehandshaking is used, the RTS signal indicates to the DCE that the host canreceive data.CTS Clear to Send - Output from Modem - A “handshaking” signal which isasserted by the DCE (TTL low) when it has enabled communications andtransmission from the DTE can commence. When hardware handshaking isused, 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 bekept in mind when looking at signals relative to the modem (DCE); the modemtransmits 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.
48 MHX-920 Operating Manual: Appendix B Serial Interface
MHX-920 Operating Manual: Appendix C Sample Schematic Diagram 49C. Sample Schematic DiagramThe following is a sample microprocessor implementation with a MICROCHIP PIC 16C74 and the MHX-920. The MHX-920performs no level shifting on the serial port, so direct connection to the host microprocessor is possible.DO NOT CONNECT THE MHX-920 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-920. The bi-directional Port D is used for asserting or monitoring control signals from the MHX-920.The RESET signal is a momentary active low signal asserted by the host microprocessor.RESET initializes the MHX-920 and places the system in a known state. This signal should be set high after the hostmicroprocessor has been reset.RXDTXDDCDDTRDSRRTSCTSRESETPIC16C74MHX-920231467831Power Connections not shownRC7RC6RD0RD1RD2RD3RD4RD5RD6
50 MHX-920 Operating Manual: Appendix C Sample Schematic Diagram
MHX-920 Operating Manual: Appendix D. Factory Default Settings 51D. Factory Default SettingsAT&F1 - Master Default SettingsE1, Q0, V1, W0, S0=1, S2=43, S3=13, S4=10, S5=8DCD &C1 (On)DTR &D0 (DTR is ignored)Framing &E0 (Disabled)Handshaking &K3 (Enabled)DSR &S1 (On in Data, Off in Command)Operating Mode S101=1 (Master P-MP)Serial Baud Rate S102=7 (9600 baud)Wireless Link Rate S103=2 (Fast, No FEC)Network Address S104=1Unit Address S105=1Primary Hop Pattern S106=0Encryption Key S107=1Output Power S108=2 (100mW)Hop Interval S109=4Data Format S110=1 (8N1)Packet Minimum Size S111=1Packet Maximum Size S112=43Packet Retransmissions S113=1Packet Size Control S114=0Packet Repeat Interval S115=1 (Don’t Care)Character Timeout (ms) S116=8Modbus Mode S117=0Roaming S118=0Quick Enter to Command S119=1RTS/DCD Framing (ms) S120=0DCD Timeout (ms) S121=0Remote Control S122=0Secondary Hop Pattern S206=2 (Don’t Care)Packet Retry Limit S213=2 (Don’t Care)AT&F2 - Slave Default SettingsE1, Q0, V1, W0, S0=1, S2=43, S3=13, S4=10, S5=8DCD &C1 (On)DTR &D0 (DTR is ignored)Framing &E0 (Disabled)Handshaking &K3 (Enabled)DSR &S1 (On in Data, Off in Command)Operating Mode S101=3 (Slave)Serial Baud Rate S102=7 (9600 baud)Wireless Link Rate S103=2 (Fast, No FEC) (Set by Master)Network Address S104=1Unit Address S105=2Primary Hop Pattern S106=0Encryption Key S107=1Output Power S108=2 (100mW)Hop Interval S109=4 (Set by Master)Data Format S110=1 (8N1)Packet Minimum Size S111=1Packet Maximum Size S112=43Packet Retransmissions S113=1 (Don’t Care)Packet Size Control S114=0Packet Repeat Interval S115=1Character Timeout (ms) S116=8Modbus Mode S117=0Roaming S118=0Quick Enter to Command S119=1RTS/DCD Framing (ms) S120=0DCD Timeout (ms) S121=0Remote Control S122=0Secondary Hop Pattern S206=2 (Don’t Care)Packet Retry Limit S213=2AT&F3 - Repeater Default SettingsE1, Q0, V1, W0, S0=1, S2=43, S3=13, S4=10, S5=8DCD &C1 (On)DTR &D0 (DTR is ignored)Framing &E0 (Disabled)Handshaking &K3 (Enabled)DSR &S1 (On in Data, Off in Command)Operating Mode S101=4 (Repeater)Serial Baud Rate S102=7 (9600 baud)Wireless Link Rate S103=2 (Fast, No FEC) (Set by Master)Network Address S104=1Unit Address S105=3Primary Hop Pattern S106=0Encryption Key S107=1Output Power S108=2 (100mW)Hop Interval S109=4 (Set by Master)Data Format S110=1 (8N1)Packet Minimum Size S111=1Packet Maximum Size S112=43Packet Retransmissions S113=1Packet Size Control S114=0Packet Repeat Interval S115=1Character Timeout (ms) S116=8Modbus Mode S117=0Roaming S118=0Quick Enter to Command S119=1RTS/DCD Framing (ms) S120=0DCD Timeout (ms) S121=0Remote Control S122=0Secondary Hop Pattern S206=2Packet Retry Limit S213=2AT&F4 -Slave Through Repeater Default SettingsE1, Q0, V1, W0, S0=1, S2=43, S3=13, S4=10, S5=8DCD &C1 (On)DTR &D0 (DTR is ignored)Framing &E0 (Disabled)Handshaking &K3 (Enabled)DSR &S1 (On in Data, Off in Command)Operating Mode S101=3 (Slave)Serial Baud Rate S102=7 (9600 baud)Wireless Link Rate S103=2 (Fast, No FEC) (Set by Master)Network Address S104=1Unit Address S105=4Primary Hop Pattern S106=2Encryption Key S107=1Output Power S108=2 (100mW)Hop Interval S109=4 (Set by Master)Data Format S110=1 (8N1)Packet Minimum Size S111=1Packet Maximum Size S112=43Packet Retransmissions S113=1 (Don’t Care)Packet Size Control S114=0Packet Repeat Interval S115=1Character Timeout (ms) S116=8Modbus Mode S117=0Roaming S118=0Quick Enter to Command S119=1RTS/DCD Framing (ms) S120=0DCD Timeout (ms) S121=0Remote Control S122=0Secondary Hop Pattern S206=2 (Don’t Care)Packet Retry Limit S213=2
52 MHX-920 Operating Manual: Appendix D Factory Default Settings
MHX-920 Operating Manual: Appendix E. Performance Tables 53E. Performance TablesThe scope of this appendix is to find the best possible performance and maximum packet size at different modes ofoperation. 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 optimalpacket size. .HopIntervalOptimal Packet Size (bytes)Throughput(kbps)*1 (8 ms) 14 20Slave <--> Master 2 (12 ms) 66 52Communication. 3 (16 ms) 110 66(No Repeater) 4 (20 ms) 154 745 (30 ms) 255 83Link Rate 6 (45 ms) 255 56S103=2 7 (80 ms) 255 318 (120 ms) 255 211 (8 ms) 5 4Slave <--> Master 2 (12 ms) 34 22Communication. 3 (16 ms) 54 28(No Repeater) 4 (20 ms) 76 325 (30 ms) 130 38Link Rate 6 (45 ms) 210 43S103=4 7 (80 ms) 255 308 (120 ms) 255 201 (8 ms) N/A N/ARepeater <--> 2 (12 ms) 3 1Master Direct 3 (16 ms) 22 13Communication. 4 (20 ms) 44 215 (30 ms) 101 32Link Rate 6 (45 ms) 178 39S103=2 7 (80 ms) 255 318 (120 ms) 255 211 (8 ms) N/A N/ARepeater <--> 2 (12 ms) N/A N/AMaster Direct 3 (16 ms) 5 2Communication. 4 (20 ms) 16 65 (30 ms) 43 12Link Rate 6 (45 ms) 80 16S103=4 7 (80 ms) 174 208 (120 ms) 255 201 (8 ms) N/A N/ASlave <--> Master 2 (12 ms) 3 1Through One or 3 (16 ms) 22 13More Repeaters. 4 (20 ms) 43 215 (30 ms) 93 31Link Rate 6 (45 ms) 174 38S103=2 7 (80 ms) 255 318 (120 ms) 255 211 (8 ms) N/A N/ASlave <--> Master 2 (12 ms) N/A N/AThrough One or 3 (16 ms) N/A N/AMore Repeaters. 4 (20 ms) 14 65 (30 ms) 40 12Link Rate 6 (45 ms) 80 16S103=4 7 (80 ms) 174 198 (120 ms) 255 20
54 MHX-920 Operating Manual: Appendix E. Performance Tables
MHX-920 Operating Manual: Appendix F. Hopping Patterns 55F. Hopping PatternsThis Appendix provides a guide for selecting appropriate hopping patterns (S106,S206). Thereare 64 hopping patterns: The first 62 come pre-programmed from the factory as per the tablebelow. There are 31 patterns in Group A and 31 in Group B. When deploying a network, it isrecommended that you use choose hopping patterns all belonging to the same group. Patternshave been designed to notch out certain segments of the ISM band.Pattern Number Spectrum Used0, 2, 4, 6, 8, 10, 12 902.4 - 927.6 MHz14, 16, 18, 20 905.2 - 924.8 MHzGroup A 22, 24, 26, 28 908.0 - 927.6 MHzPatterns 0,2,4...60 30, 32, 34, 36 902.4 - 907.2, 913.2 - 927.6 MHz38, 40, 42, 44 902.4 - 912.4, 918.4 - 927.6 MHz46, 48, 50, 52 902.4 - 917.4, 923.6 - 927.6 MHz54, 56, 58, 60 902.4 - 922.0 MHz1, 3, 5, 7, 9, 11, 13 902.6 - 927.4 MHz15, 17, 19, 21 905.4 - 925.0 MHzGroup B 23, 25, 27, 29 907.8 - 927.4 MHzPatterns 1,3,5...61 31, 33, 35, 37 902.6 - 907.4, 913.0 - 927.4 MHz39, 41, 43, 45 902.6 - 912.6, 918.2 - 927.4 MHz47, 49, 51, 53 902.6 - 917.8, 923.4 - 927.4 MHz55, 57, 59, 61 902.6 - 922.2 MHzPatterns 58 to 63 -may be manually entered or edited by entering AT&H at the Command Line, and following theprompts. Each pattern must use a channel only once, and must consist of exactly 50 channels. There are 127channels available ranging from Channel 1 at 902.4 MHz up to Channel 127 at 927.6 MHz.
56 MHX-920 Operating Manual: Appendix F. Hopping Patterns
MHX-920 Operating Manual: Appendix G. Technical Specifications 57G. Technical SpecificationsElectrical/PhysicalData Interface Asynchronous Serial Port, TTL LevelsSignals Sig. Gnd, TX, RX, DCD, DSR, DTR, RTS, CTSBandwidth / Data Rate 2,400 - 115,200 bps, uncompressed half-duplex,Approx. 85 kbps sustained in intelligent asymmetrical full-duplextransmission modeCommunications Range130 kilometres (19 miles)Power Requirements 5 VDC, 1.0 AmpPower Consumption 600 mA max, 300 mA typical at 1W transmit; 200 mA receiveOperating Frequency 902-928 MHzSystem Gain 135 dBSensitivity -105 dBmOutput Power 1, 10, 100, 1000mW (user-selectable)Spreading Code Frequency HoppingHopping Patterns 64 pseudo-random, user-selectableError Detection CRC-16 with auto re-transmitError Correction User-selectable Forward Error Correction (FEC)Adjacent Channel Rejection > 60 dBIn-band Rejection > 70 dBOut-of-band Rejection > 80 dBDimensions (LxWxH) Encl: 3.5” x 2.1” x 1.” (90 mm x 53 mm x 25 mm)Weight 75 gramsOperating Environment Temperature: -40 to +70°CHumidity: 5 to 95%, non-condensingStorage Temperature -40 to 90°C1. Clear line-of-sight, elevated high-gain antennas.
58 MHX-920 Operating Manual: Appendix H. Mechanical Drawings
MHX-920 Operating Manual: Appendix H. Mechanical Drawing 59H. Mechanical Drawing21003500dia. 901701254507506001900100 225200275Dimensions in thousandths of an inch.Shaded areas = keep clear. Microhard Systems Inc.MHX Series Mechanical Drawing#110, 1144 - 29th Ave. N.E.Calgary, Alberta, CanadaT2E 7P1Rev.2Size A Document Number: D1042-02 Drawn By: NB Sheet 1 of 1Friday, July 14, 2000800Top ViewPin 12021 40
60 MHX-920 Operating Manual: Appendix H. Mechanical Drawings
MHX-920 Operating Manual: Appendix I. Glossary 61I. GlossaryTerminology Used in the MHX-920 Operating ManualAsynchronous communications A method oftelecommunications in which units of single bytesof data are sent separately and at an arbitrary time(not periodically or referenced to a clock). Bytesare “padded” with start and stop bits to distinguisheach as a unit for the receiving end, which neednot be synchronized with the sending terminal.Attenuation The loss of signal power throughequipment, lines/cables, or other transmissiondevices. Measured in decibels (dB).Bandwidth The information-carrying capacity of adata transmission medium or device, usuallyexpressed in bits/second (bps).Baud Unit of signaling speed equivalent to thenumber of discrete conditions or events persecond. If each signal event represents only onebit condition, then baud rate equals bits persecond (bps) – this is generally true of the serialdata port, so baud and bps have been usedinterchangeably in this manual when referring tothe serial port; this is not always the case duringthe DCE-to-DCE communications, where anumber of modulation techniques are used toincrease the bps rate over the baud rate.Bit The smallest unit of information in a binarysystem, represented by either a 1 or 0.Abbreviated “b”.Bits per second (b/s or bps) A measure of datatransmission rate in serial communications. Alsosee baud.Byte A group of bits, generally 8 bits in length. Abyte typically represents a character of data.Abbreviated “B”.Characters per second (cps) A measure of datatransmission rate for common exchanges of data.A character is usually represented by 10 bits: an 8-bit byte plus two additional bits for marking thestart and stop. Thus, in most cases (but notalways), cps is related to bits per second (bps) bya 1:10 ratio.CRC (Cyclic Redundancy Check) An error-detectionscheme for transmitted data. Performed by usinga polynomial algorithm on data, and appending achecksum to the end of the packet. At thereceiving end, a similar algorithm is performedand checked against the transmitted checksum.Crossover cable (Also known as rollover, null-modem, or modem-eliminator cable) A cablewhich allows direct DTE-to-DTE connectionwithout intermediate DCEs typically used tobridge the two communicating devices. Can alsobe used to make cabled DCE-to-DCE connections.The name is derived from “crossing” or “rolling”several lines, including the TX and RX lines sothat transmitted data from one DTE is received onthe RX pin of the other DTE and vice-versa.Data Communications Equipment (DCE, alsoreferred to as Data Circuit-TerminatingEquipment, Data Set) A device which facilitates acommunications connection between DataTerminal Equipment (DTEs). Often, two or morecompatible DCE devices are used to “bridge”DTEs which need to exchange data. A DCEperforms signal encoding, decoding, andconversion of data sent/received by the DTE, andtransmits/receives data with another DCE.Common example is a modem.Data Terminal Equipment (DTE) An end-device which sends/receives data to/from a DCE,often providing a user-interface for informationexchange. Common examples are computers,terminals, and printers.dBm Stands for “Decibels referenced to onemilliwatt (1 mW)”. A standard unit of powerlevel commonly used in RF and communicationswork. n dBm is equal to 10(n/10) milliwatt, so0dBm = 1mW, -10dBm = 0.1mW, -20dBm =0.01mW, etc.DCE See Data Communications Equipment.DTE See Data Terminal Equipment.Flow Control A method of moderating thetransmission of data so that all devices within thecommunications link (DTEs and DCEs) transmitand receive only as much data as they can handleat once. This prevents devices from sending datawhich cannot be received at the other end due toconditions such as a full buffer or hardware not ina ready state. This is ideally handled by hardwareusing flow-control and handshaking signals, but
62 MHX-920 Operating Manual: Appendix I . Glossarycan be controlled also by software using X-ON/X-OFF (transmitter on/off) commands.Frequency-hopping A type of spread spectrumcommunication whereby the carrier frequencyused between transmitter and receiver changesrepeatedly in a synchronized fashion according toa specified algorithm or table. This minimizesunauthorized jamming (interference) andinterception of telecommunications.Full-duplex Where data can be transmitted,simultaneously and independently, bi-directionally.Half duplex Exists when the communicationsmedium supports bi-directional transmission, butdata can only travel in one direction at the sametime.Handshaking A flow-control procedure forestablishing data communications wherebydevices indicate that data is to be sent and awaitappropriate signals that allow them to proceed.Line-of-sight Condition in which a transmittedsignal can reach its destination by travelling astraight path, without being absorbed and/orbounced by objects in its path.Master The station which controls and/or polls oneor more Slave stations in a point-to-point or point-to-multipoint network. Often functions as a serveror hub for the network.Non-volatile memory Memory which retainsinformation which is written to it.Null modem cable See Crossover cable.Point-to-point A simple communications networkin which only two DTEs are participants.Point-to-multipoint A communications networkin which a Master DTE communicates with two ormore Slave DTEs.Repeater A device which automatically amplifiesor restores signals to compensate for distortionand/or attenuation prior to retransmission. Arepeater is typically used to extend the distancefor which data can be reliably transmitted using aparticular medium or communications device.RS-232 (Recommended Standard 232; moreaccurately, RS-232C or EIA/TIA-232E) Definedby the EIA, a widely known standard electricaland physical interface for linking DCEs and DTEsfor serial data communications. Traditionallyspecifies a 25-pin D-sub connector, althoughmany newer devices use a compact 9-pinconnector with only the essential signaling linesused 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 termdescribing a DTE device which is part of a wide-area network. Often a RTU performs data I/O andtransmits the data to a centralized station.Serial communications A common mode ofdata transmission whereby character bits are sentsequentially, one at a time, using the samesignaling line. Contrast with parallelcommunications where all bits of a byte aretransmitted at once, usually requiring a signal linefor each bit.Shielded cable Interface medium which isinternally shrouded by a protective sheath tominimize external electromagnetic interference(“noise”).Slave A station which is controlled and/or polled bythe Master station for communications. Typicallyrepresents one end of a point-to-point connection,or one of the terminal nodes in a point-to-multipoint network. Often a RTU is linked by aSlave DCE.Spread spectrum A method of transmitting asignal over a wider bandwidth (using severalfrequencies) than the minimum necessary for theoriginally narrowband signal. A number oftechniques are used to achieve spread spectrumtelecommunications, including frequency hopping.Spread spectrum provides the possibility ofsharing the same band amongst many users whileincreasing 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 communicationsystem, often expressed as bits or characters persecond (bps or cps).

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