Microhard Systems 98P001X01 Wireless Modem User Manual MRX900 Manua

Microhard Systems Inc Wireless Modem MRX900 Manua

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Contents

1. Users Manual and Operation Description
2. Modified Users Manual
3. Part 15 statement and RF Exposure warning statement

Modified Users Manual

MRX-900 Operating Manual: Contents iContents1. Introduction1.0 Product Overview ....................................................................................................................................... 11.1 Features....................................................................................................................................................... 11.2 About this Manual....................................................................................................................................... 22. Initial Installation and Setup2.0 Unpacking and Inspection........................................................................................................................... 32.1 Additional Requirements ............................................................................................................................ 32.2 Connectors and Indicators........................................................................................................................... 42.3 Hardware Setup........................................................................................................................................... 42.4 Configuration .............................................................................................................................................. 52.4.1 Quick Start Approach....................................................................................................................... 5A. Point-to-Point ............................................................................................................................. 5B. Point-to-Multipoint..................................................................................................................... 63. Configuration Options3.0 Changing Parameters in Configuration Menu............................................................................................. 73.1 Operating Mode .......................................................................................................................................... 73.2 Serial Baud Rate ......................................................................................................................................... 93.3 Wireless Link Rate...................................................................................................................................... 93.4 Network Address....................................................................................................................................... 103.5 Unit Address ............................................................................................................................................. 103.6 Hopping Pattern ........................................................................................................................................ 103.7 Encryption Key ......................................................................................................................................... 113.8 Output Power Level .................................................................................................................................. 113.9 Packet Parameters..................................................................................................................................... 123.10 Radio Statistics.......................................................................................................................................... 133.11 Slave List .................................................................................................................................................. 13AppendicesA. MRX-900 Configuration Menu Navigation Chart ................................................................ 15B. Configuration Record............................................................................................................ 17C. RS-232 Interface and CablesC.0 RS-232 Line Signals ................................................................................................................................. 19C.1 DTE-to-DCE (Straight-Through) Cables.................................................................................................. 19C.2 Crossover / Null Modem Cables............................................................................................................... 20C.3 Loopback Plug .......................................................................................................................................... 20D. Surface or Wall Mounting..................................................................................................... 21E. Troubleshooting..................................................................................................................... 23F. Technical Specifications........................................................................................................ 25G. Glossary................................................................................................................................. 27

ii MRX-900 Operating Manual

MRX-900 Operating Manual: Introduction. 11. Introduction1.0 Product OverviewCongratulations on choosing the MRX-900 wireless modem! Your newMRX-900 is a state-of-the-art, 900 MHz frequency-hopping spread-spectrumcommunications transceiver. Equipped with the MRX-900, terminal devices(DTEs) up to 30 km (or more)1 apart will be capable of establishing high-speed2 communications wirelessly.Once properly installed and configured, a pair of MRX-900s provides apractical and reliable alternative to using traditional analog phone-linemodems or “null-modem” serial cable (RS-232) connections for datacommunications between terminal equipment. Moreover, wireless datacommunications using the MRX-900 means you will benefit from:ngreater flexibility and freedom to relocate terminal equipment,nreduced cabling hassles,neliminated requirement for access to wire-based transfer mediasuch as telephone lines,nthe ability to communicate through walls, floors, and manyother obstacles.While the MRX-900 is handsomely sleek and compact in its design, itdelivers power and convenience and offers quality and dependability.The MRX-900’s versatility makes it the ideal solution for applicationsranging from office-productivity to industrial data control and acquisition.While a pair of MRX-900 modems can link two terminal devices (“point-to-point” operation), multiple MRX-900 units can be used together to create anetwork of various topologies (“point-to-multipoint” operation). Multipleindependent networks can operate concurrently, so it is possible for unrelatedcommunications operations to take place in the same or a nearby area withoutsacrificing privacy, functionality, or reliability.1.1 FeaturesKey features of the MRX-900 include:ntransmission within a public, license-exempt band of the radiospectrum3 – this means there are no conditions on usage of theMRX-900, and that it can be used without restrictions or accessfees (such as those incurred by cellular airtime);na fully compliant RS-232 serial I/O data port with handshakingand hardware flow control, allowing the MRX-900 to interfacewith virtually any terminal device with an asynchronous RS-232port, such as a computer; 1Ideal conditions with clear line-of-sight communications, using high-gain antennas.2Up to 115,200 bits per second (bps).3902-928 MHz, which is license-free within North America; may need to be factory-configureddifferently for some countries.

2MRX-900 Operating Manual: Introductionntwenty different user-selectable pseudo-random hoppingpatterns to offer the possibility of separately operating multiplenetworks while providing security, reliability and high toleranceto 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 MRX-900 can be used as adrop-in replacement for most null-modem cable (DTE-to-DTE)operations, and as a modem replacement with minimal or nosoftware changes.While the typical application for the MRX-900 is to provide a mid- to long-range wireless communications link between DTEs, it can be adapted toalmost any situation where an RS-232 asynchronous serial interface is usedand data intercommunication is required.1.2 About this ManualThis manual has been provided as a guide and reference for installing andusing MRX-900 wireless modems. The manual contains instructions,suggestions, and information which will help you set up and achieve optimalperformance from your equipment using the MRX-900.Although the manual is intended for all MRX-900 users from the novice tothe professional, it is recommended that new users of the MRX-900thoroughly read Chapters 2 and 3, which describe the initial setup andconfiguration of the modems. Also, it may be noteworthy to review sectionsof Chapter 4 which are relevant to your application while providing helpfulhints for optimizing your MRX-900 modems. The Appendices, including theGlossary of Terms, are provided as informational references which you mayfind useful throughout the use of this manual as well as during the operationof 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 MRX-900 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 MRX-900, and please remember to send in your warrantyregistration!

MRX-900 Operating Manual: Initial Setup and Configuration. 32. Initial Setup and Configuration2.0 Unpacking and InspectionThe following items should be found in the shipping carton. Inspect themodem and accessories for damage. Report damages or shortages to thedistributor from which the unit was purchased. Keep all packing materials inthe event that transportation is required in the future.Package contents (normal distribution):1MRX-900 Wireless Modem 12 6” Rubber Ducky Antenna 139 VDC, 1 Amp Power Adapter 14Operating Manual (this document) 1The materials you received may vary from those depicted in the figures,which should be referred to only as a guideline.2.1 Additional RequirementsSince the MRX-900 is a unique product in a class of its own, it willcommunicate only with another MRX-900 which has been compatiblyconfigured. Thus, at least two MRX-900s will be required to establish awireless communications link. Each MRX-900 will also require access to a120 VAC power source.Additionally, the following requirements should be taken into considerationwhen preparing to install your MRX-900 wireless modem. These represent“typical” requirements, but due to the large variation of user needs andapplications, the items are user-supplied and are not accessories whichnormally ship with the MRX-900. However, most of these are readilyavailable from any electronics or computer retailer, or they can be orderedthrough your distributor for Microhard Systems’ products.nShielded “straight-through” RS-232 cable (typically DB9P-to-DB9S or DB9P-to-DB25S) for each MRX-900 to DTEconnection*.nConnection adapters and converters, if necessary (e.g., gender-changers, DB9-to-DB25 adapters, etc.)nTerminal device (e.g., PC or laptop) with functional RS-232 portand appropriate communications (terminal emulation) software.n Mounting hardware (screws) if surface or wall mounting isdesired (see Appendix D for mounting information) *Note: DB9P denotes a 9-position D-sub male connector (with pins), while DB9Sdenotes the mating connector of female gender (with sockets).Although the physical space required for the MRX-900 is minimal, youshould ensure that there is sufficient room for access to the unit’s rear panel(where connectors and indicators are located), as well as for an antenna to beconnected (typically oriented in an upright/vertical position).

4MRX-900 Operating Manual: Initial Setup and ConfigurationCaution: Using any other powersupply which does not provide theproper voltage or current coulddamage the MRX-900 and voidyour warranty. Doing so is at yourown risk.2.2 Connectors and IndicatorsLocate the rear panel of the MRX-900. The interface connectors andindicator lights are summarized below. This manual will refer to these itemsin the sections that follow.9 VDC Input - It is recommended that the provided power adapter be used tosupply power to the MRX-900 via this connector, although anycompatible DC power source which has an output of 9 volts and at least 1amp may be used.Receive Signal Strength Indicator (RSSI) LEDs - These LEDs show thequality/strength of the received signal. As the signal strength increases,the LEDs will illuminate incrementally from bottom to top.RS-232 Data Port (DCE) - The socketed (female) D-sub connector is used tointerface the MRX-900 to a DTE device and operates at 2400 to 115,200bps. The same port is used to configure the modem by interfacing to aterminal (at 9600 bps). See Appendix C for details on the RS-232interface and line signals.Configuration Button - This button is used to configure the modem. Whendepressed for about 2-3 seconds, the configuration menu will be initiatedand displayed on the connected terminal (DTE) screen. Subsequentinteraction with the modem is performed using the terminal keyboard.Receive LED - Lights up when the modem receives data over the wireless link,as well as during internal carrier search and synchronization operations.Transmit LED - Lights to indicate that the modem is transmitting data wire-lessly. This light flashes during initial startup and carrier synchronization.Antenna Connector - Reverse-polarity TNC connector for connecting anycompatible antenna, including the provided rubber-ducky antenna.2.3 Hardware SetupPrior to setting up and configuring the MRX-900, please observe therequirements outlined in Section 2.1. When you are ready for the initialsetup:1. Connect the modem to a terminal or personal computer (DTE) using astandard serial cable. Depending on the connector on your DTE device, youwill typically need a DB9-to-DB9 or DB9-to-DB25 cable (see Appendix Cfor additional information). Connect the male DB9 end of the cable to theMRX-900 data port.2. Apply power to the MRX-900 by plugging the provided adapter into thepower input socket, and the other end into an active 120 VAC outlet. (Youwill see the Receive LED illuminate to indicate that it is operating normally.)3. On your terminal or in your terminal program (e.g. HyperTerminal inMicrosoft Windows or Procomm Plus from Datastorm Technologies), ensurethat the correct port is selected and that it has been configured for a speed of9600 baud and a data format of 8N1 (8 bits, No parity, 1 stop bit). Althoughno terminal emulation is necessary, TTY can be selected if desired.4. You are now ready to configure the modem for operation. The followingsections will walk you through the procedure.

MRX-900 Operating Manual: Initial Setup and Configuration. 52.4 ConfigurationPrior to establishing a wireless link, each MRX-900 that will participate inthe link must be correctly configured for compatibility and for the desiredmode of operation.The two most common types of networks used are:nPoint-to-point: A master station communicates with a singleslave station.nPoint-to-multipoint: A master station communications withtwo or more slave stations.Within any network, the master will communicate only with slave(s) assignedto the same network. Similarly, a slave will only communicate with themaster of the network to which it is assigned.The quick configuration procedure is outlined below for each of these modes.2.4.1 Quick Start ApproachAssuming your hardware has been properly setup (as outlined in Section 2.3)for configuration, you are now ready to begin the process. Start by locatingthe Configuration Button at the rear of your MRX-900 and pressing it for twoto three seconds. A menu similar to the following should appear on yourterminal screen: Microhard Systems Inc MRX-900 Configuration1) Operating Mode Slave - Point to Point2) Serial Baud Rate 1152003) Wireless Link Rate Turbo4) Network Address 15) Unit Address 16) Hopping Pattern A7) Encryption Key 08) Output Power Level 1 mW9) Packet ParametersA) Radio StatsESC to exitSelect an Item to Configure : _The minimum configuration requirements for point-to-point and point-to-multipoint are summarized below. These requirements will get you startedand only ensure that a link can be established, but do not necessarily providethe best performance; optimization of the communications link is discussedin later sections.A. Point-to-PointTo establish a point-to-point communications link, the following requisitesmust be satisfied:nThe Operating Mode for one modem must be configured as a“Master - Point-to-Point”, and the other as a “ Slave - Point-to-Point”.nThe Serial Baud Rate for each modem must be set to match thebaud rate of the connected equipment (DCE and DTE rates must beequivalent).

6MRX-900 Operating Manual: Initial Setup and ConfigurationWarning: Using an antenna otherthan one approved by MicrohardSystems Inc. could result inundesired performance, and maydamage the MRX-900. Failure touse an approved antenna may voidyour warranty. It is the user’sresponsibility to ensure theantenna has adequate lightningprotection.nThe Wireless Link Rate for both modems must be the same.nThe Network Address assigned for both modems must be thesame.nThe Unit Address assigned for both modems must be the same.nThe same Hopping Pattern must be selected for both modems.nBoth modems must use the same Encryption Key.B. Point-to-MultipointTo establish a point-to-multipoint network, the following requisites must besatisfied:nThe Operating Mode for one modem must be configured as aPoint-to-Multipoint Master, and the others as Point-to-Multipoint Slaves.nThe Serial Baud Rate for each modem must be set to match thebaud rate of the connected equipment (DCE and DTE rates must beequivalent).nThe Wireless Link Rate for all modems must be the same.nThe Network Address assigned to all modems must be the same.nEach Slave must be assigned a unique Unit Address.nThe Master must have a list of all Slave Unit Numbers in its SlaveList.nThe same Hopping Pattern must be selected for all modems.nAll modems must use the same Encryption Key.Each of the parameters above are defined using the terminal to display themenu-driven configuration screens and setting the appropriate items. Settingsare immediately stored in non-volatile memory upon selection, and aretherefore retained even after powering down. Each item and the settableparameters within the modem configuration are described in detail in Chapter3: Configuration Options. Once the configuration is complete, the modemscan be restored to operation mode by either pressing ESC to exit the menu(“Running ...” should then appear), or simply by power-cycling the unit(momentarily disrupting power to the unit, then restoring it).2.5 Checking the LinkOnce configured properly, a pair or set of communicating modems can be testedto ensure that a link can be successfully established. Attach the provided antennato the antenna connector on each MRX-900 and screw the antenna in snugly.The modems should indicate the status of the wireless link via the RSSILEDs on the rear panel: if the link is good, up to three LEDs shouldilluminate; and if the link is absent (due to a fault at one end or another, suchas misconfiguration), the LEDs will be unlit. It is recommended that ifMRX-900s will be deployed in a field where large distances separate DTEs,the modems be configured and tested in close proximity (e.g., in the sameroom) first to ensure a good link can be established and settings are correct.This will facilitate troubleshooting, should problems arise.

MRX-900 Operating Manual: Configuration Options 73. Configuration OptionsIn configuration mode, thedefault serial rate for theMRX-900 is 9600 baud.Refer to Appendix A (page15) for a menu navigationchart to facilitate use of theconfiguration menus.Configuration options areimmediately stored in non-volatile memory whenselected and become activeafter exiting configuration orpower-cycling the unit.3.0 Configuration ParametersThe MRX-900 is easily configured to meet a wide range of needs andapplications. Configuration is fully menu-driven and requires only a terminalwith a 9600 baud RS-232 port. Configuration mode is initiated by depressingthe Configuration Button on the back panel of the MRX-900 and holding itfor at least two or three seconds. The main configuration menu is thendisplayed: Microhard Systems Inc MRX-900 Configuration1) Operating Mode Slave - Point to Point2) Serial Baud Rate 1152003) Wireless Link Rate Turbo4) Network Address 15) Unit Address 16) Hopping Pattern A7) Encryption Key 08) Output Power Level 1 mW9) Packet ParametersA) Radio StatsESC to exitSelect an Item to Configure : _Note that 9600 baud is the default rate for configuration only, and that theactual data communications rate during operation is user-defined, with ratesfrom 2400 to 115,200 bps. (With reference to the serial data port, baud andbps can correctly be used interchangeably since no modulation occurs toincrease the bit rate over the baud rate. This may not always be the case withmodulated signals transmitted between DCEs.) No terminal emulation isrequired, although a “TTY” setting can be used if mode selection is requiredby your communications software.Most menu items are hot-key driven, requiring minimal keypresses to quicklynavigate and set parameters. Current parameters are indicated to the right ofeach item in the main configuration menu (see above), and preceded by anasterisk (*) for each chosen option in parameter submenus (shown onfollowing pages). Configuration parameters are saved in non-volatilememory as soon as they are selected. This allows quick configuration of themodem and reactivation in operation mode by either pressing ESC on theterminal from the main configuration menu, or simply power-cycling the unit(momentarily disconnecting power to the MRX-900).3.1 Operating ModeThe Operating Mode partly defines the “personality” of the MRX-900.When item 1 is chosen from the configuration menu, the following optionsare available:

8MRX-900 Operating Manual: Configuration OptionsEach unit must be either aMaster, Slave, or Repeater.Only one Master can existfor each network.Operating Mode* 1) Master - Point to Point 2) Slave - Point to Point 3) Master - Point to Multipoint 4) Slave - Point to Multipoint 5) RepeaterESC to exitSelect Operating Mode : _Each unit should be configured as a Master or Slave, except when it is usedas a Repeater. The user should decide, prior to deployment, whether a point-to-point or point-to-multipoint network is appropriate for the application, andhow each unit will be assigned to terminals.1) Master - Point to Point One unit in a point-to-point linkshould be set as the Master, obligating the other modem to be used as aSlave. During operation, it makes little difference which end is which,especially if data is generally transmitted unidirectionally at any givenmoment. In cases where both DTEs will generally transmit large amounts ofdata simultaneously, the Master should be assigned to the terminal whosetransmit priority is higher. When both terminals have data to send, morebandwidth is dynamically allocated to the Master; otherwise, the transmittingend, whichever it is at the time, is given the full bandwidth.2) Slave - Point to Point The terminal in a point-to-pointnetwork which is not set as the Master, is obligated to be the Slave. TheSlave will communicate with the Master, either directly or through a repeater,whose network address, unit address, and hopping pattern matches its own.3) Master - Point to Multipoint In a point-to-multipointnetwork, one unit should be set as the Master, obligating all other modems tobe Slaves. The Master designation is generally given to the station whichfunctions as a hub for all remote nodes, and it is the Master station’sresponsibility to control communications with Slaves. When this mode isselected, an additional option, “B) Slave List”, will appear in the mainmenu. The Master, using its Slave List, will communicate with Slaves on thesame network in a round-robin fashion. Setting up the Slave List will bedescribed in more detail later.4) Slave - Point to Multipoint Several Slaves exist in a point-to-multipoint network, all of which communicate with the common Master.Each slave may communicate with the Master directly, through a repeater ofits own, or via a common repeater. Slaves cannot directly communicate withother Slaves.5) Repeater The Repeater mode is chosen when the unit will function asneither a Master nor a Slave, but as an intermediary in a Master-Slave(s)relationship. The Repeater is useful when the direct Master-to-Slavetransmission distance exceeds the maximum range or transmission ishindered due to environmental or geographical conditions. A repeater canserve one or more slaves much like the point-to-multipoint master. When thismode is selected, an additional option, “B) Slave List”, will appear inthe main menu. Setting up the Slave List will be described in more detaillater.

MRX-900 Operating Manual: Configuration Options 93.2 Serial Baud RateThe Serial Baud Rate is the speed that the DTE communications port will beset at during normal operation. This rate has no bearing on the serial rateduring configuration, which is always performed at 9600 baud. The possibleparameters after selecting item 2 from the configuration menu are:Serial Baud Rate* 1) 115200 2) 57600 3) 38400 4) 28800 5) 19200 6) 14400 7) 9600 8) 7200 9) 4800 A) 3600 B) 2400ESC to exitSelect Serial Baud Rate : _It 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. It is important that the rate specifiedin the MRX-900 configuration matches that of the DTE to which it isconnected, or the DTE-DCE communication will fail.3.3 Wireless Link RateThe Wireless Link Rate is the speed and optimization method for whichmodems will communicate over the RF link. The possible settings are:Wireless Link Rate* 1) Turbo 2) Fast 3) NormalESC to exitSelect Wireless Link Rate : _Depending on the application requirements, each mode will provide differentthroughputs and performance optimizations as follows:Mode Expected Performance(Maximum Throughput) Primary OptimizationTurbo 115.2 kbps Optimized for SpeedFast 57.6 kbps Optimized for Distance and SpeedNormal 28.8 kbps Optimized for DistanceGenerally, the lowest rate which provides sufficient bandwidth should beselected. For example, if DTEs are set to communicate at 19.2 kbps, then thewireless rate can be set to Normal (with the added advantage of slightlygreater range). If DTEs will typically require nearly 115.2 kbps of sustainedbandwidth, then the wireless rate should be set to Turbo (setting it lowerwould “bottleneck” data transmissions in the wireless link). Note that there isa slight compromise between speed performance and range.

10 MRX-900 Operating Manual: Configuration OptionsSelect a Network Addressand assign it to all unitswhich will be included in thenetwork.Use the same Unit Addresson all units for point-to-pointmode. In multipoint mode,set all slaves to a uniqueUnit Address.Ensure that all units within anetwork use the samehopping pattern, and thatmultiple concurrent networkseach have different hoppingpatterns.3.4 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 networkusing the same hardware. As well, the Network Address provides a measureof privacy and security. Only those units which are members of the networkwill participate in the communications interchange. Valid values for theNetwork Address range from 0 to 65535, inclusive. Choosing the optionfrom the main menu (option 4) will yield something like the following, afterwhich up to five digits can be entered, followed by Enter or Return:Network Address = 39513ESC to exitSet Network Address : _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.3.5 Unit AddressIn point-to-point operation, the Unit Address on all units (Master, Slave, andRepeater, if applicable) must be the same. In a multipoint system, the UnitAddress uniquely identifies each Slave from the others. This parameter,whose value can range from 0 to 65535 inclusive, is set in parallel with theSlave List (described later), so the Unit Address for each slave should benoted and subsequently added to the Slave List. The parameter is set byselecting item 5 in the configuration menu, and entering up to five digitsfollowed by the Enter or Return key:Unit Address = 23ESC to exitSet Unit Address : _Remember that each Slave should have a Unit Address which is unique fromany other Slave in the network.3.6 Hopping PatternSince the MRX-900 is a frequency-hopping modem, the carrier frequencychanges periodically according one of twenty pseudo-random patterns,selected by defining the Hopping Pattern. When this option (#6) is chosenfrom the configuration menu, something resembling the following appears:Hopping Pattern = AESC to exitSet Hopping Pattern [A..T] :A letter from A to T, inclusive, can be used to select the pattern. It isimportant that all units which will participate in a network use the samehopping pattern, or the communication link will fail.

MRX-900 Operating Manual: Configuration Options 11Test the communicationslink using a low power leveland work upward. Avoidusing a higher power thannecessary since performancemay actually degrade.Warning: When transmittingat the full power of 1W, FCCregulations prohibit using anantenna with a gain greaterthan 6 dBi (6 dB aboveisotropic gain).3.7 Encryption KeyThe Encryption Key provides a measure of security and privacy ofcommunications by rendering the transmitted data useless without the correctkey on the receiver. By selecting option 7 from the configuration menu, youare prompted to enter a key (valid values range from 0 to 65535), followedby Return or Enter:Encryption Key = 6109ESC to exitSet Encryption Key : _Keep in mind that all units within the network must use the same key forcommunications to succeed.3.8 Output Power LevelThe Output Power Level determines at what power the MRX-900 transmits.The super-sensitive MRX-900 can operate with very low power levels, so itis recommended that the lowest power necessary is used; using excessivepower contributes to unnecessary “RF polution”. To set the power level,select option 8 from the configuration menu and select one of the following:Power Output Level 1) 1 mW 2) 10 mW 3) 100 mW* 4) 1000 mW 5) AdaptiveESC to exitSelect Power Output Level : _Ideally, 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 each setting aredescribed 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 outdoor conditions, up to 30 km or more can be achieved.Note that only an antenna with a gain of no more 6 dBi may be used.Any higher is a violation of FCC rules.Adaptive Used in noisy environments where interference may vary. Powermay change over time. Note that only an antenna with a gain of nomore 6 dBi may be used. Any higher is a violation of FCC rules.

12 MRX-900 Operating Manual: Configuration OptionsIn an ideal situation wherethe communications linkperforms well and there is nointerfering “noise” that cancause errors, set theMinimum Size to 0 andMaximum Size to 255.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 gainincluding cabling losses cannot exceed 36 - 30 = 6 dBi. If an antennawith a gain higher than 6 dBi were to be used, the power setting must beadjusted appropriately.All MRX-900 products purchased with an antenna having a gain greaterthan 6 dBi will be factory-pre-configured to disable the 1W powersetting, thereby making 100 mW the maximum transmitted power.3.9 Packet ParametersPacket Parameters define the characteristics of the internal packets or frameswhich are transmitted. The settings should be set only by an expert sinceadequate care must be taken to maintain reliability and optimumperformance. .The parameters which can be set are displayed under option 9in the main menu:Packet Parameters1) Minimum Size 02) Maximum Size 2553) Retry Limit 2554) CRC/Retransmit EnabledESC to exitSelect a Parameter to Configure : _1) Minimum Size This setting has a range of 0 to 255, and defines thenumber of bytes to accumulate from the DTE before transmitting a packet.Setting this value to 0 ensures that all characters sent by the DTE areimmediately transmitted. The value may not exceed the maximum packetsize.2) Maximum Size This setting has a range of 1 to 255, and defines themaximum number of bytes from the DTE which should be encapsulated in apacket. This value should be greater than the minimum packet size, but notsmaller than is necessary for reliable communications. If the wireless link isconsistently good and solid, a maximum size of 255 is recommended.However, if the link is poor (e.g., experiencing excessive interference) anddata is frequently retransmitted, the maximum packet size should be reduced.This decreases the probability of errors within packets, and reduces theamount of traffic in the event that retransmissions are required. Since asmaller packet size results in a proportionally higher overhead and loweroverall throughput on a good connection, this should only be reduced if manyerrors are being detected by CRC (see Radio Statistics option ofconfiguration).

MRX-900 Operating Manual: Configuration Options 133) Retry Limit This determines the number of attempts that will bemade to retransmit data which failed the CRC checksum. Once the limit isreached, the modem will give up and discard the data. If the wirelessconnection is poor and data often needs to be retransmitted, a modem couldbe “tied up” trying to retransmit, thus holding up pending data. (XXX)4) CRC/Retransmit This parameter is either Enabled or Disabled, anddetermines whether the MRX-900 will handle error-checking and manageretransmissions (to guarantee accuracy of data, possibly at the cost ofthroughput), or whether these functions will be handled by the software oneach DTE. When this parameter is selected, the following submenu isdisplayed:CRC/Retransmit* 1) Enabled 2) DisabledESC to exitSelect CRC usage : _3.10 Radio StatisticsThis option (selection A) displays a list of performance statistics for the unitsince it was powered up. Note that this information is only available ifconfiguration is not initiated immediately after a power-up cycle; loss ofpower will reset the statistics. The information report resembles thefollowing:Radio Statistics Number of header packets transmitted: 4920 Number of data packets transmitted: 5933 Number of errors detected by CRC: 1 Average RSSI: 64Press any keyNumber of header packets transmitted: Gives an indicationof the number of header packets transmitted since power-up and is used fortroubleshooting. This value increases from 0 to 65535, at which point it“wraps around” to 0 again.Number of data packets transmitted: Gives an indication ofthe number of data packets transmitted since power-up and is used fortroubleshooting. This value increases from 0 to 65535, at which point it“wraps around” to 0 again.Number of errors detected by CRC: Each packet transmittedby the MRX-900 includes a checksum against which the data on the receivingend is checked. If the CRC values do not match, an error event is added tothe total error count since power-up. This statistic is only available if CRCerror detection is enabled, and gives a measure of the quality of the wirelessconnection. Note that when errors are detected, the sending modemretransmits the packet so errors are never observed at the DTE.

14 MRX-900 Operating Manual: Configuration OptionsAverage RSSI: Indicates the average strength of the RF connection forthe period since power-up. Values may have values in the following ranges: RSSI Meaning < 50 Marginal link, may yield poor performance 50-60 Satisfactory link 60-70 Good link, should generally provide adequate performance 70-80 Strong link, typically very good performance > 80 Very strong link3.11 Slave ListThis option (B) only appears if the unit has been set up as a Point-to-Multipoint Master or as a Repeater. When selected, the following submenuwill become available:Slave List1) Add Slave2) Delete Slave3) Show List4) Clear ListESC to exitSelect an operation : _1) Add Slave Selecting this option subsequently prompts for a slaveaddress: “Add Slave Address : _“. Enter a value from 0 to 65535which corresponds to a Slave Unit Address, followed by Enter/Return. Usecare to ensure the value is correctly entered since there is no way for theMaster or Repeater to validate the entry. Up to 255 Slaves may be added tothe Slave List.2) Delete Slave This operation is used to reverse the action of option1, removing a previously-entered slave from the Slave List. When selected,the prompt, “Delete Slave Address : _” appears. A value from 0to 65535 should be entered, followed by Enter/Return.3) Show List This option displays the current list of slaves, eachseparated by a comma, similar to the following:Select an operation : 3List of Slaves00001, 00002, 00020, 00032, 000504) Clear List This option removes all slaves from the Slave List, andshould be used with caution. It is an alternative to repetitively using option 2for each Slave in the list. When selected, you are prompted with thefollowing: “Clear the entire slave list? (Y) _”. Pressing“Y” will clear the entire list, while pressing any other key will exit and abortthe command.

MRX-900 Operating Manual: The Configuration Menus 15A. The Configuration MenusThe following chart provides an “at-a-glance” overview of the menus available when configuring the MRX-900, aswell as the valid parameters for each item.MRX-900 Configuration Quick-ReferenceConfiguration Main MenuOperatingMode Serial BaudRate WirelessLink RateMaximumSize TimeoutIntervalPower OutputLevel SlaveListRadioStatsPacketParametersRetryTimeout1) 1152002) 576003) 384004) 288005) 192006) 144007) 96008) 72009) 4800A) 3600B) 24001) Master - Point to Point2) Slave - Point to Point3) Master - Point to Multipoint4) Slave - Pont to Multipoint5) Repeater0-65535 A-T 0-655351) Turbo2) Fast3) Normal1) 1mW2) 10 mW3) 100 mW4) 1000 mW (1W)UnitAddress HoppingPattern EncryptionKeyDeleteSlave ShowList ClearList(2) (3)(1) (4)(2) (3)(1) (4)(2)(1) (3) (5)(4) (6) (7) (8) (9) (A) (B)

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MRX-900 Operating Manual: Configuration Record 17B. Configuration RecordThe following tables are provided as a convenient way to record the configuration of your MRX-900s for futurereference. You may wish to copy or adapt it for your use.MRX-900 Record of Configurationo Point-to-Point OperationUnit Mode UnitAddress Output PowerLevel Serial Baud Rate WirelessLink Network Address(0 - 65535) Hopping Pattern(A - T) Encryption Key(0 - 65535) Master S/N: _________ o 1 mW o 10 mW o 100 mW o 1000 mW (1W) o 115200 o 57600 o 38400 o 28800 o 19200 o 14400 o 9600 o 7200 o 4800 o 3600 o 2400 Slave S/N: _________ o 1 mW o 10 mW o 100 mW o 1000 mW (1W) o 115200 o 57600 o 38400 o 28800 o 19200 o 14400 o 9600 o 7200 o 4800 o 3600 o 2400 o Turbo o Fast o Normal Repeater S/N: _________ o 1 mW o 10 mW o 100 mW o 1000 mW (1W)

18 MRX-900 Operating Manual: Configuration Recordo Point-to-Multipoint OperationUnit Mode Address Output PowerLevel Serial Baud Rate WirelessLink Network Address(0 - 65535) Hopping Pattern(A - T) Encryption Key(0 - 65535) Master S/N: _________Slave List: o 1 mW o 10 mW o 100 mW o 1000 mW (1W) o 115200 o 57600 o 38400 o 28800 o 19200 o 14400 o 9600 o 7200 o 4800 o 3600 o 2400 Slave S/N: _________UniqueUnit Address(0-65535): o 1 mW o 10 mW o 100 mW o 1000 mW (1W) o 115200 o 57600 o 38400 o 28800 o 19200 o 14400 o 9600 o 7200 o 4800 o 3600 o 2400 Slave S/N: _________UniqueUnit Address(0-65535): o 1 mW o 10 mW o 100 mW o 1000 mW (1W) o 115200 o 57600 o 38400 o 28800 o 19200 o 14400 o 9600 o 7200 o 4800 o 3600 o 2400 Slave S/N: _________UniqueUnit Address(0-65535): o 1 mW o 10 mW o 100 mW o 1000 mW (1W) o 115200 o 57600 o 38400 o 28800 o 19200 o 14400 o 9600 o 7200 o 4800 o 3600 o 2400 Slave S/N: _________UniqueUnit Address(0-65535): o 1 mW o 10 mW o 100 mW o 1000 mW (1W) o 115200 o 57600 o 38400 o 28800 o 19200 o 14400 o 9600 o 7200 o 4800 o 3600 o 2400 o Turbo o Fast o Normal Slave S/N: _________UniqueUnit Address(0-65535): o 1 mW o 10 mW o 100 mW o 1000 mW (1W) o 115200 o 57600 o 38400 o 28800 o 19200 o 14400 o 9600 o 7200 o 4800 o 3600 o 2400 Slave S/N: _________UniqueUnit Address(0-65535): o 1 mW o 10 mW o 100 mW o 1000 mW (1W) o 115200 o 57600 o 38400 o 28800 o 19200 o 14400 o 9600 o 7200 o 4800 o 3600 o 2400 Repeater S/N: _________Slave List: o 1 mW o 10 mW o 100 mW o 1000 mW (1W) Repeater S/N: _________Slave List: o 1 mW o 10 mW o 100 mW o 1000 mW (1W) Repeater S/N: _________Slave List: o 1 mW o 10 mW o 100 mW o 1000 mW (1W)

MRX-900 Operating Manual: RS-232 Interface and Cables 19C. RS-232 Interface and Cables“Straight-through”DB9-to-DB9RS-232 CableModem(DCE)9-pin male SignalTerminal(DTE)9-pin1 DCD →12 RX →23← TX  34← DTR  45 SG →56 DSR →67← RTS  78 CTS →89(n/c) (n/c) 9“Straight-through”DB9-to-DB25RS-232 CableModem(DCE)9-pin male SignalTerminal(DTE)25-pin1 DCD →82 RX →33← TX  24← DTR  205 SG →76 DSR →67← RTS  48 CTS →59(n/c)Arrows denote the direction thatsignals are asserted (e.g., DCDoriginates at the DCE and tells theDTE that a carrier is present).C.0 RS-232 Line SignalsThe MRX-900 uses a 9-pin D-sub connector for asynchronous serial I/O.The pin assignments conform to standard RS-232 signals, so a common serialcable can be used for interfacing the MRX-900 to most DTE devices.Line signals in the RS-232 interface are described below:DCD Data Carrier Detect - When set high, DCD informs the DTE that acommunications link has been established with another MRX-900.RX Receive Data - Signals transferred from the MRX-900 are received by theDTE via RX.TX Transmit Data - Signals are transmitted from the DTE via TX to theMRX-900DTR Data Terminal Ready - Raised to an active level by the DTE to inform themodem 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 - Set high by the modem (DCE, or “data set” as it wasformerly called) to inform the DTE that it is alive and ready forcommunications. DSR is the modem’s equivalent of the DTR signal.RTS Request to Send - A “handshaking” signal which is asserted by the DTE whenit is ready to transmit data. (Typically, the DCE responds by activating CTS.)Essentially, RTS is the DTE’s way of saying, “I am ready to send datawhenever you are.”CTS Clear to Send - A “handshaking” signal set active by the DCE when it hasenabled communications and transmission from the DTE can commence.CTS is usually asserted after the DCE has detected a RTS signal from theDTE. It is the modem’s way of saying, “Go ahead, I am ready for your 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 the most common application, is a device such as a computer.C.1 DTE-to-DCE (Straight-Through) CablesDue to the variety of cabling requirements by each user of the MRX-900,interface cables required for DTE-to-DCE connection are user-supplieditems. Unless the RS-232 port or connector on the DTE deviates from thecommon pin assignments, it is recommended that pre-fabricated shieldedcables (and interface adapters, if necessary) be purchased for your applicationto ensure optimal performance and reliability. In cases where an RJ-45 DTEtermination is required, the cable will need to be designed according to theDTE’s RJ-45 pinout; this 8-position connector has no standard assignment ofsignals and varies greatly between devices and manufacturers.If cables must be fabricated, the wiring diagrams provided should be used.For best results, it is recommended that cables be no longer than necessary tointerface the DTE and DCE (up to about 25 feet).

20 MRX-900 Operating Manual: RS-232 Interface and Cables“Crossover” / “Null”DB9-to-DB9RS-232 Cable9-pin 9-pin1,64233241,65578879(n/c)(n/c)9“Crossover” / “Null”DB9-to-DB25RS-232 Cable9-pin 25-pin1,620223346,85775849(n/c)(n/c)9“Crossover” / “Null”DB25-to-DB25RS-232 Cable25-pin 25-pin11233245546,82077206,8Note that in all cases, the DSR andDCD lines are tied together (lines 1and 6 for DB9; 6 and 8 for DB25).DCE DB9 Loopback Plug9-pin maleconnector1(n/c)2345(n/c)6789(n/c)C.2 Crossover / Null Modem CablesTypically, establishing a DTE-to-DCE connection is achieved using astraight-through cable as described earlier. In some instances, generallywhen a direct DTE-to-DTE or DCE-to-DCE connection is desired, acrossover cable (also known as rollover, null-modem, or modem-eliminatorcable) is used. Using a straight-through cable will not workIn a DTE-to-DTE connection, the crossover cable essentially functions bydeceiving each DTE into “thinking” that it is connected to a modem.Similarly, a DCE connected to a DCE “believes” it is connected to a DTE.The data transmission is handled such that transmitted data (TX) from onedevice is driven to the receive data line (RX) of the other. RTS is associatedwith CTS. Since a DCE in a typical DTE-to-DCE connection usually mustindicate its own online status (via DSR) as well as its connection to anotherDCE (via DCD), these are relayed together as a ready-state indicator from theDTE via DTR.Wiring diagrams for the most common cables of this type are provided foryour reference.C.3 Loopback PlugOccasionally, you may wish to perform diagnostic or benchmark tests on thedata transmission between two MRX-900s. A common test is the loopback,whereby an MRX-900, connected to a DTE, communicates with anotherMRX-900, whose serial port has been fitted with a DCE loopback plug. Byso doing, all data sent by the DTE should be wirelessly transmitted to theremote MRX-900, which echoes back the data to the originator, namely theDTE. Essentially the same data is transmitted twice: once to the remotemodem, and the second time as it is re-transmitted back from the remotemodem. Such tests are useful for testing the performance of the wireless link,including throughput, bit error rate, packet loss, and a number of othermeasures.The wiring for a basic 9-pin DCE loopback plug is provided, which can beconstructed simply by tying together pins 2 and 3, as well as 7 and 8, on amale DB9 connector.Testing that a DTE serial port is functional is often achieved easily by using aDTE loopback plug, which can be constructed similarly to the DCE loopbackplug for a 9-pin connector. The gender is often different (use a femaleconnector for use on a common PC), but the same pins are tied together: 2with 3, and 7 with 8. Additionally, pins 4 and 6 should be tied together. (Fora 25-pin DTE loopback plug, connect pins 2 with 3, 4 with 5, and 6 with 20.)

MRX-900 Operating Manual: Surface or Wall Mounting 21D. Surface or Wall MountingThe drill template and dimensional figure below has been provided to facilitate placement in case you wish to mount yourMRX-900. Make a copy of the template at 100% scale and drill through the paper at each of the cross-hairs. Screw headsshould be no larger than 5/16” diameter, with outer screw shaft of no more than about 1/8”. If mounted with the rubber footprinton bottom of unit, about 1/4” clearance should be left between surface and bottom of screw head; otherwise, unit can be mountedflush with surface. Ensure that there is adequate clearance around unit, including room for cables and antenna.1.85”0.25”3.57”4.22”ANT.SERIALDrill holes for mounting byusing this template.Place template on wallor surface and drill holesat each “+”, using a 1/16”bit for wood.0.15”0.32”

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MRX-900 Operating Manual: Troubleshooting 23E. TroubleshootingHere are solutions to some of the common problems and symptoms that may be experienced.————————————Problem: I am trying to set up the MRX-900 but I cannot get the configuration menu to appear.Solutions: 1. Make sure you are depressing the Configuration Button for at least 2 or 3 seconds. TheConfiguration Menu, by design, only shows up after the button has been held briefly to preventunintentional triggering.2. Check that the power adapter is snugly inserted into the power input jack, and that the AC-outlet islive. You can verify that the MRX-900 is operational and that it is receiving power by thecontinuous illumination of the receive LED.3. Ensure that your RS-232 cable is the correct type – that it is a straight-through rather than a crossoveror null-modem cable, and that it is the correct cable for your terminal. Also ensure that the matingconnectors are seated properly.4. Verify that you are using the correct data port and that it is configured properly (this check may beaided by use of a DTE-loopback plug, as explained in section C.3). Ensure that the software has thecorrect communications settings for configuration: 9600 bps, 8 bits, no parity, 1 stop bit (8N1). Ifthe serial communications between the MRX-900 and your terminal is working correctly, aninitialization message should appear each time you power up the unit.————————————Problem: I have configured my MRX-900s, but I cannot achieve a communications connection. The RSSI LEDsare unlit.Solutions: 1. Ensure that the Wireless Link Rate, Network Address, and Hopping Pattern are the same for all units.If using the modems in multipoint operation, ensure that each Slave has a unique Unit Address andthey are included in the Slave List of Repeaters (if applicable) and of the Master. In point-to-pointmode, ensure the Unit Address on both Master and Slave are the same. Once these settings arecorrect, the RSSI LEDs should illuminate when communicating units are powered up.2. The power level is too high or too low for the current arrangement of MRX-900s. First, ensure thatantennas are properly and snugly connected. If the units are in very close proximity (within severalfeet) and the power level is too high, they will be saturated and may not operate efficiently.Conversely, if the modems are far away from each other or there are many obstacles between them, ahigher level may be required for the modems to pick up each other’s signal.————————————Problem: I have configured my MRX-900s, but I cannot achieve a communications connection. The RSSI LEDsare lit.Solutions: 1. Verify that the serial baud rate between each MRX-900 and its connecting DTE are the same.2. Isolate the problem by directly connecting the DTEs using a crossover cable and setting the portspeeds on both ends the same. If this fails, then the problem is most likely attributable to theDTE/software application, and use of the MRX-900 in this circumstance will also fail. If the hardwire connection is successful, then the problem may be a cabling issue. Ensure that all cables arestraight-through RS-232 cables and that they are connected properly to all devices.————————————Problem: I have the serial data ports on both my DTEs and MRX-900s set the same, but I cannot achieve athroughput near serial rate I’ve set up.Solutions: 1. Verify that the Wireless Link Rate on all modems are set to a rate which provides a wireless linkhigher than the serial links, since a lower wireless rate will “bottleneck” the communications link.

24 MRX-900 Operating Manual: Troubleshooting2. If you are using an MRX-900 as a Repeater, it will cut the effective throughput roughly in halfbecause of its “store and forward” nature; the repeater spends half of its time receiving data and theother half transmitting the received data.3. Although some high speed rates are achieved under ideal conditions, various factors may reduce theeffective speed. This includes external RF (radio frequency) interference from sources such ascellular telephones and base stations. When the airwaves are “noisy”, errors can be introduced intothe data stream which force the modems to retransmit (if CRC-16 error detection is turned on),consequently compromising effective throughput. Possible solutions include use of high-gain(directional) antennas or relocation of antennas if possible (higher, and possibly a few feet laterally).————————————Problem: I seem to keep losing characters and/or received data is not the same as transmitted data over myMRX-900sSolutions: 1. By enabling CRC-16 error detection, the MRX-900s will automatically detect lost or corrupted dataand will resend packets to ensure accuracy. Check to see that this option is enabled (recommended)and see if the situation improves.2. If CRC-16 error detection is enabled and this problem is occurring, it is likely due to the linkbetween the MRX-900 and the DTE device, or the DTE device itself. Possible causes of thisinclude:a) unshielded and/or too long a serial cable - try replacing the cable with one that is shorter, andensure it is shielded, particularly if the environment in which the equipment resides is subject toelectromagnetic interference.b) absence of a 16550 UART on the DTE serial port - if the equipment being used is older, it mayhave an 8250 or other UART which does not provide adequate buffering capabilities, especiallyat rates higher than 9600 baud. Try replacing the serial interface driver chip or serial card ifpossible and high-speed communications is necessary. Otherwise, a lower serial baud rate (onboth the modem and DTE) may help cure the problem.c) if operating in a multi-tasking environment, the processor may not be fast enough to handlemultiple processes or threads while keeping up with the flow of serial data - if possible, reducethe number of concurrently-running processes, or retry the operation in a single-task environment.Alternatively, try lowering the serial baud rate (modem and DTE) to a speed that the DTE cankeep up with.————————————

MRX-900 Operating Manual: Troubleshooting 25F. Technical SpecificationsElectrical/PhysicalData Interface Asynchronous RS-232, 9-pin female D-subSignals Sig. Gnd, TX, RX, DCD, DSR, DTR, RTS, CTSBandwidth / Data Rate 2,400 - 115,200 bps, uncompressed half-duplex,Approx. 100 kbps sustained in intelligent asymmetrical full-duplextransmission modeCommunications Range130 kilometres (19 miles)Power Requirements 9.0 VDC, 1.0 AmpPower Consumption 600 mA at 1 W transmit, 200 mA receiveOperating Frequency 902 - 928 MHzSystem Gain 135 dBSensitivity -105 dBmOutput Power 1mW, 10mW, 100mW, 1W (user-selectable or adaptive)Spreading Code Frequency HoppingHopping Patterns 20 pseudo-random, user-selectableError Detection CRC-16 with auto re-transmitEnclosure material Milled aluminum, raven-black baked powder coat finishDimensions (WxDxH) Encl: 3.72” x 4.25” x 1.72” (94.5 mm x 108.0 mm x 43.7 mm)With extrusions (mounting legs, rear connectors):4.72” x 5.25” x 1.72” (119.9 mm x 133.4 mm x 43.7 mm)Weight 420 grams (with included antenna)Operating Environment Temperature: -30 to +60°CHumidity: 5 to 95%, non-condensingStorage Temperature -40 to 90°C1. Clear line-of-sight, elevated high-gain antennas.

26 MRX-900 Operating Manual

MRX-900 Operating Manual: Glossary 27G. GlossaryTerminology Used in the MRX-900 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 hardware

28 MRX-900 Operating Manual: Glossaryusing flow-control and handshaking signals, butcan 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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