FX MS/TP Communications Bus TechnicalBulletinBuilding Technologies & 1670

2FX MS/TP Communications Bus Technical Bulletin

ContentsContentsDocument Introduction. 5Summary of Changes. 5FX Related Documentation. 5MS/TP Bus Overview. 6FC Bus. 7SA Bus. 8End-of-Line Termination on the MS/TP Bus. 8Baud Rates on the MS/TP Bus. 9Device Addressing on the MS/TP Bus. 9Setting a Device Address. 10Rotary switch dials. 12Enabling FX-PC Controllers for Wireless Operation. 13Local FC Bus Rules and Specifications. 13End-of-Line Termination on Local FC Bus. 16EOL Terminator Module. 17SA Bus Rules and Specifications. 19SA Bus Device Limits. 19End-of-Line Termination on SA Bus. 20SA Buses with Multiple Network Sensors. 21MS/TP Bus Cable Recommendations. 21Screw Terminal Blocks for Connecting FC and SA Bus Cables. 23Grounding the MS/TP Bus Cable Shield. 24RJ-Style Modular Jack and Cables for SA Bus. 25Commissioning Devices on the MS/TP Bus. 26Peer-to-Peer Communication. 26Appendix: FC Bus Auxiliary Devices. 26Repeaters. 26Configuring Repeaters. 27Fiber-Optic Modems. 28Routing and Connecting the Fiber Cables. 28Connecting Modems to MS/TP Bus. 29Fiber Modem between Two Segments. 29Setting Termination on Fiber Modems. 30Surge Protectors. 31Appendix: Maximizing and Troubleshooting the MS/TP Bus. 35Maximizing Tips. 35Parameters that affect MS/TP communication. 36Duplicate addresses. 36Common problems. 36Correcting physical bus problems. 38FX MS/TP Communications Bus Technical Bulletin3

Correcting bus overload problems. 38Appendix: Integrating 2-wire BACnet devices on a common MS/TP bus with JCI 3-wire devices. 39Appendix: Optimizing SA Bus Traffic. 39Excessive Traffic. 40Inputs and COVs. 40Outputs and Commands. 42SA Bus Traffic Reduction. 43Product warranty. 44Software terms. 44Single point of contact. 44Contact information. 444FX MS/TP Communications Bus Technical Bulletin

Document IntroductionThe BACnet protocol MS/TP communications bus is a local network that connects supervisorycontrollers and field controllers to field point interfaces.This document describes the specifications, device limits, and rules of the MS/TP communicationsbus, as well as how to wire and terminate devices, and troubleshoot device communication onthe MS/TP bus. The remote MS/TP field bus is also described. With the addition of a BACnet IP toBACnet MS/TP Router, the Remote Field Bus allows connection to remote equipment controllersover IP.This document is intended for the user who needs to know the rules, requirements, limits,specifications, and configuration of the MS/TP bus to design, wire, or troubleshoot an MS/TPapplication.Summary of ChangesThe following information is new or revised: Document updated to include the new I/O expansion modules (F4-XMP) and supervisorycontroller (F4-SNC) Document updated to include the new WRG1830/ZFR183x Pro Wireless Field Bus SystemFX Related DocumentationThe following table lists the related documentation that describes controllers and systems relatedto the MS/TP communications bus.Table 1: Related DocumentationFor Information OnInstallation and specifications of the FXSupervisory ControllerSpecifications of the Facility ExplorerSystem Field ControllersSpecifications of the F4-CGM GeneralPurpose Application ControllersSpecifications of the F4-CVM VAVTerminal Equipment ControllersSpecifications of the F4-XPM ExpansionModulesSee DocumentFX Supervisory Controller InstallationInstructionsFX-PC Programmable Controllers andRelated Products Product BulletinF4-CGM General Purpose ApplicationControllers Installation InstructionsF4-CVM VAV Terminal EquipmentControllers Installation InstructionsF4-XPM Expansion Modules InstallationGuideFX-PCG16 General Purpose ProgrammableInstallation and specifications of the FX- Controller Installation InstructionsPCG16 or FX-PCG26FX-PCG26 General Purpose ProgrammableController Installation InstructionsFX-PCV Programmable VAV BoxProgrammable Variable Air Volume BoxControllers Installation InstructionsInstallation and specifications of the FX- PCV1615 and PCV1630 ProgrammablePCVVariable Air Volume Box ControllersInstallation InstructionsFX-PCV1930 VAV Controller InstallationInstructionsFX MS/TP Communications Bus Technical BulletinLIT or Part NumberPart No. 24-10051-0LIT-12011657Part No. 24-10143-01787Part No. 24-10143-01809Part No. 24-10143-02155Part No. 24-10143-152Part No. 24-10143-144Part No. 24-10143-179Part No. 24-10143-357Part No. 24-10143-015235

Table 1: Related DocumentationFor Information OnSee DocumentLIT or Part NumberFX-PCX17 and FX-PCX27 Expansion Input/Part No. 24-10144-106Output Module Installation InstructionsFX-PCX37 Expansion Input/Output ModulePart No. 24-10144-114Installation InstructionsFX-PCX47 Expansion Input/Output ModulePart No. 24-10144-122Installation and specifications of the FX- Installation InstructionsPCX Expansion ModulesFX-PCX2721 Expansion Input/OutputPart No. 24-10144-173Module Installation InstructionsFX-PCX3731 Expansion Input/OutputPart No. 24-10144-181Module Installation InstructionsFX-PCX3721 Expansion Input/OutputPart No. 24-10144-203Module Installation InstructionsFX-PCA2611-0 Advanced ApplicationProgrammable Controller InstallationPart No. 24-10143-403InstructionsFX-PCA2612-1 Advanced ApplicationProgrammable Controller InstallationPart No. 24-10143-268Installation and specifications of the FXInstructionsPCA Series ControllersPCA3613 Advanced ApplicationProgrammable Controller InstallationPart No. 24-10143-1175InstructionssFX-PCA4911 Advanced ApplicationPart No. 24-10143-01531Controller Installation GuideIntegrating BACnet MS/TP and BACnetIP devices into the FX SupervisoryFX Workbench User's GuideLIT-12011149ControllersInstallation of and specifications for theMS-BACEOL-0 RS-485 End-of-LineMS-BACEOL-0 End-of-Line TerminatorPart No. 24-10264-4Terminator Installation InstructionsModuleApplications, features, and benefits ofWRG1830/ZFR183x Pro Series Wireless Fieldthe WRG1830/ZFR Series Wireless FieldLIT-1901026Bus System Catalog PageBus SystemLIT-12011147Note: This LIT number representsa printer-friendly version of theHelp.Controller Configuration Tool SoftwareController Tool HelpInstalling the F4-SNCF4-SNC Installtion GuideFX80 Supervisory Controller InstallationInstructionsInstalling the FX80Part No. 24-10143-02031Part No. 24-10143-861MS/TP Bus OverviewThe BACnet protocol MS/TP communications bus is a local network that connects supervisorycontrollers and equipment controllers to field point interfaces. The bus is based on BACnetstandard protocol ANSI/ASHRAE Standard 135.The BACnet MS/TP protocol is a peer-to-peer, multiple master protocol based on token passing.Only master devices can receive the token, and only the device holding the token is allowed tooriginate a message on the bus. The token is passed from master device to master device usinga small message. The token is passed in consecutive order starting with the lowest address.Subordinate devices on the bus only communicate on the bus when responding to a data requestfrom a master device.An MS/TP bus is used for two types of buses: a Field Controller bus (FC) and a Sensor Actuator (SA)bus (Figure 1).6FX MS/TP Communications Bus Technical Bulletin

The FC bus and SA bus are networks of daisy-chained devices. Each bus has only one bussupervisor, depending on which controllers are connected. On a local FC bus, the bus supervisor isthe supervisory controller. On the local SA bus, the bus supervisor is a field controller.The bus supervisor communicates with devices on the supervised bus and with devices on the next(higher level) bus on the network. The bus supervisor typically starts the communication on the FCbus or SA bus. If an SA bus or FC bus does not have a bus supervisor, the master device with thelowest device address value on the bus and a specific baud rate selected starts the communication.The WRG1830/ZFR183x Series Wireless Field Bus System enables wireless communication on anMS/TP bus, allowing you to create wireless connections between General Purpose ApplicationControllers (CGMs), VAV Terminal Equipment Controllers (CVMs), Expansion Modules (XPMs),General Purpose Programmable Controllers (PCGs), Input/Output Modules (PCXs), AdvancedApplication Programmable Controller (PCAs), Programmable Variable Air Volume Box Controller(PCVs), and supervisory devices such as the FX80 and FX-SNC.See Enabling FX-PC Controllers for Wireless Operation and for detailed information about theWRG1830/ZFR183x Series Wireless Field Bus System.FC BusAn FC Bus connects an FX Supervisory Controller to CVM, CGM, XPM, or FX-PC Series ProgrammableControllers and TEC26xx or TEC30xx Series Thermostat Controllers. On an FC Bus, the FXSupervisory Controller is the bus supervisor.Figure 1: Example of an MS/TP Communications BusAn FC bus supports up to three bus segments that are connected with network repeaters (Figure 6).See Local FC Bus Rules and Specifications for more information.FX MS/TP Communications Bus Technical Bulletin7

SA BusThe SA bus connects CGM, CVM, SNC and FX-PC devices to endpoint devices, such as FX-PCXExpansion I/O Modules, XPM Expansion Modules, network sensors, FX-DIS Local ControllerDisplays, FX-TAD and Johnson Controls Variable Speed Drives (VSDs).On an SA bus, a CGM, CVM, SNC, or FX-PC controller is the bus supervisor. The SA bus is a privateMS/TP bus that only supports those devices that can be defined using the Controller ConfigurationTool (CCT) programming tool. The bus does not support bus segments (Figure 10). See SA BusRules and Specifications for more information.End-of-Line Termination on the MS/TP BusDaisy-chained RS485-protocol networks typically require some type of end-of-line (EOL) terminationto reduce interference caused by signal reflection that occurs when data transmissions reachthe end of a bus segment and bounce back on the segment. The high baud rates on MS/TP busapplications require robust EOL termination and strict adherence to the EOL termination rules.Figure 2 shows an example of the EOL termination settings on an MS/TP bus application.The EOL termination requirements for the FC bus are different from the SA bus requirements.See End-of-Line Termination on Local FC Bus and End-of-Line Termination on SA Bus for moreinformation.Also, third-party MS/TP devices and TEC30xx Series thermostats have different EOL terminationrequirements from Facility Explorer devices on the FC bus. See for more information.Figure 2: EOL Terminations on an MS/TP Bus8FX MS/TP Communications Bus Technical Bulletin

Baud Rates on the MS/TP BusAn MS/TP bus can be configured to communicate at one of four different baud rates. All of thedevices on an MS/TP bus must communicate at the same baud rate.The baud rate setting determines the rate at which devices communicate data over the bus. Thebaud rate settings available on Facility Explorer MS/TP devices are 9600 bps, 19.2 kbps, 38.4 kbps,76.8 kbps, and Auto. The baud rate setting for Facility Explorer devices is set in the software.Note: The BACnet Standard only requires support for 9600 and 38400 baud. Some third-partyvendor devices might not support all the baud rates supported by the FX system. Reducing thebaud rate to accommodate these devices affects overall performance.We recommend setting all MS/TP bus supervisors FX Supervisory Controllers or BACnet Routers to38,400.We recommend setting all CGM and CVM controllers, XPM modules or FX-PC controllers on the FCbus (FX-PCGs, FX-PCAs, FX-PCVs, and FX-PCXs) to Auto. In the Auto setting, the FX devices listen forthe bus supervisor to communicate first; the devices then automatically set their baud rate to thebus supervisor’s baud rate. CGM and CVM controllers, XPM modules and FX-PC controllers ship witha default baud rate setting of Auto.If you anticipate critical peer-to-peer communication and therefore do not want equipmentcontrollers to wait for the bus supervisor to establish the baud rate, you can specify the baud ratefor each device immediately at startup. Choose the baud rate carefully if you use this method, sincechanging it requires changing each device separately.Typically, the baud rate setting on bus repeaters and third-party MS/TP devices is configuredmanually at the device, and the baud rate setting must match the bus supervisor’s baudrate. A third-party device that does not support auto-baud establishes the baud rate for theMS/TP network if the FX80 or F4-SNC is not connected. Refer to the manufacturer’s productdocumentation for information on setting the device’s baud rate.The FX software contains the following two device attributes that relate to the baud rate: Baud Rate Selection allows you to set the baud rate for the device using the CCT for CGMs,CVMs, XPMs, FX-PCGs, FX-PCAs, FX-PCVs, and FX-PCXs. Active Baud Rate allows you to view the baud rate at which the device is communicating onthe active bus when Auto baud is selected for the device.The high baud rates capable on MS/TP buses limit the range of wire gauges used on the bus. Thebaud rate, wire gauge, wire length, and the number of devices are related. Higher baud ratessupport more devices but require small gauge wire that provides lower capacitance. A lower baudrate may be required to use existing, larger gauge wire that has higher capacitance, but maysupport fewer devices. We recommend 38,400 baud using 22 AWG stranded wire. This combinationprovides the best balance between performance and installation sensitivity.For information on determining wire gauges, wire lengths, and the number of devices supported,see MS/TP Bus Cable Recommendations.Device Addressing on the MS/TP BusEach device connection on an MS/TP bus requires a device address to coordinate communication.Each bus has a set of device addresses that is separate and independent from the device addresseson all other buses. Devices connected to both an MS/TP bus and SA bus have two device addresses,one for each bus connection (Figure 3).In the MS/TP bus hierarchy, device connections on separate buses can have the same deviceaddress. For example, every bus supervisor connection on an MS/TP bus has a device address ofFX MS/TP Communications Bus Technical Bulletin9

0 (zero), and the device address for the first network sensor on any SA bus is 199. This is possiblebecause separate buses are identified with different network numbers. Figure 3 shows a simpleexample of an MS/TP bus and the device addresses for connections on the FC bus and SA bus.An FX Supervisory Controller (FX80 or F4-SNC) is the bus supervisor on an FC bus. The CGMand CVM controllers, XPM modules, or FX-PC controller is the bus supervisor on an SA bus. Thesupervisory devices have a default address of 0. Bus supervisors have a fixed device address of 0(zero) that cannot be changed (Figure 3). The current range of network sensors are all addressablewith the DIP switch set from 199 to 206 and the factory set at 199. Table 2 provides a list of the validMS/TP device address values and address value ranges for MS/TP devices.Each MS/TP master controller passes the token to the controller with the next known address. After50 token passes, each controller searches for other controllers that might have joined the networkby attempting to send the token to the controller with the next consecutive address, starting withone higher than its own, until one is found. While you do not need to address devices on the trunkconsecutively, you can improve performance by minimizing address skipping. To help with addressvalue selection, see Table 2.Note: The devices on the bus do not need to be physically wired in sequential order.Setting a Device AddressFor most devices on an MS/TP bus, the (non-supervisory) device address is set by positioning theRotary or DIP switches on the device’s address DIP switch block. The DIP switch blocks are binaryswitch blocks, with each switch representing a binary numerical value when the switch is in the ONposition. The CGM and CVM controllers have three rotary switches for setting the device address.The device address set on the address DIP switch block or rotary switches applies to the deviceconnection on the bus where the device is not the bus supervisor. For example, the rotary switcheson CGMs or CVMs and the DIP switches on FX-PCAs, FX-PCGs, or FX-PCVs (master devices) set thedevice address for the device connection to the FC bus. If the CGMs, CVMs, FX-PCAs, FX-PCGs, orFX-PCVs also supervise an SA bus, the FX-PCAs, FX-PCGs, or FX-PCVs address on an SA bus is 0 bydefault (Figure 3).A FX-PCX or F4-XPM has only one device connection, which can connect to either an FC bus or an SAbus (but not both); therefore, the device address set on a FX-PCX or F4-XPM applies to the bus towhich the FX-PCX or F4-XPM is connected. (An FX-PCX or F4-XPM is never a bus supervisor.)10FX MS/TP Communications Bus Technical Bulletin

Figure 3: MS/TP Bus Showing FC Bus and SA Bus AddressesTable 2: Valid MS/TP Bus Address Values and Address Ranges for MS/TP Bus DevicesAddress Value/ AddressClassRange0Bus Supervisor1Reserved for JCI use2Reserved for JCI use3Reserved for JCI use4–127Master RangeDevicesFC Bus: FX Supervisory Controller (FX80 or F4-SNC)SA Bus: CGMs, CVMs, F4-SNCs, FX-PCA, FX-PCG, or FX-PCVReserved for the Field Inspection Tool (FIT)Reserved for Mobile Access Portal (MAP)and ZFR/ZFRProWireless Field Bus ConverterFX-DIS1710 Local Controller DisplayFC Bus: CGMs, CVMs, XPMs, FX-PCA, FX-PCG, or FX-PCVand FX-PCXs Controllers and TEC26xx or TEC30xx SeriesThermostat ControllersSA Bus: FX-PCXs and F4-XPMs128–254Subordinate adcastFX MS/TP Communications Bus Technical BulletinSubordinate devices, VSDs, and NS network sensors on the SABus. Not Supported on the FC bus.VAV Balancing Sensor (handheld)Most NS Series Network Sensor models or VAV BalancingSensor (wall-mounted)NS Series Network SensorsDo not apply address 255 to any device.11

Important: On any FX-PCA, FX-PCG, FX-PCV, or FX-PCX that is hardwired to an MS/TP Bus,set the 128 DIP switch to the OFF position. Operating any FX-PCA, FX-PCG, FX-PCV, or FX-PCXthat is hardwired to an MS/TP Bus with the controller’s 128 DIP switch set to the ON positionresults in communication failure on the bus.As you set the device address on controllers with dip switch blocks, the best practice is to set thehighest switch value first, then the next highest switch value, and so on, until the total of the switchvalues equal the intended device address. For example, positioning switches 16, 4, and 1 to ON setsthe device address to 21 for a device on the FC bus.Figure 4: Setting the Device Address and Wireless Operation Mode on the address DIP SwitchBlockNotes: You must set switch 128 to OFF on all FX controllers that are hardwired to an FC bus. Devices may go offline momentarily when a device address is changed on an active bus. Adevice reset is not required on FX controllers or supervisory controllers after changing the MS/TP address.Some devices, such as the TEC30xx Series thermostats and third-party MS/TP devices, use theirown configuration settings to establish the device address for their connection to the bus.The graphical display model of the NS8000 as well as the TEC300 series have their addressesconfigured in software via drilling down through menus. Refer to the device manufacturer’sproduct documentation for instructions on setting the device address. The device address valuesfor TEC thermostats and all third-party devices must comply with the rules and ranges describedpreviously.Rotary switch dialsThe SNC has 3 rotary switch dials labeled Controller Number for setting the controller numberwhich can be numbered from 000 to 999. The switches are shipped from the factory set to 000. Youcan use them to set a decimal number from 000 to 999 as a unique identifier for each SNC. Thecontroller number is set using three rotary switches and may be numbered from 000 to 999. Thenumbers are ordered from left to right, most significant bit (MSB) to least significant bit (LSB) whenthe controller is oriented as shown in the following figure where the switches are set to 1 2 3.12FX MS/TP Communications Bus Technical Bulletin

Figure 5: Rotary switch device addressingEnabling FX-PC Controllers for Wireless OperationThe ZFR/ZFRPro Series Wireless Field Bus System enables wireless communication, allowing youto create wireless connections between CVM and CGM controllers, XPM expansion modules, FX-PCdevices and FX Supervisory Controllers (FX80 and F4-SNC).To operate with a ZFR Pro Series field bus, a CVM, CGM, or FX-PC Controller must be connected to aZFR Pro Wireless Field Bus Router, and the associated FX Supervisory Controllers (FX80 or F4-SNC)must be connected to a ZFR Pro Wireless Field Bus Coordinator.Local FC Bus Rules and SpecificationsTable 3, Table 4, and Figure 6 provide rules and specifications for the local FC bus.FX MS/TP Communications Bus Technical Bulletin13

Table 3: Local FC Bus Rules and LimitationsCategoryRules/LimitsSNC2515x-0x Series models can support one local FC bus.SNC1612x-0x Series models can support one local FC bus.GeneralNumber of Devices and BusSegmentsCable Length for FC Bus andBus SegmentsRecommended CableEOL TerminationFX80 Supervisory Controllers can support one or more FC Buses. Check FX SupervisoryController product literature to determine the exact number supported by specific model.CVM, CGM, and FX-PC Controllers' EOL termination and bias circuitry are much morerobust than FX Supervisory Controllers. We recommend using FX-PC Controllers at bothends of the FC Bus.SNC2515x-0x models support the following device limits on an FC bus trunk: 32SNC1612x-0x models support the following device limits on an FC bus trunk: 32The FX80 supports 32 bus segments per FC bus, 64 devices in totalBus segments on an FC bus are connected with repeaters (only). Up to two cascadedrepeaters may be applied to an FC bus (to connect three bus segments).When all of the devices connected on the FC bus are Facility Explorer devices the cablelength limits (using 22 AWG 3-wire twisted, shielded cable) are as follows: Each bus segment can be up to 1,220 m (4,000 ft) in length. Each FC bus can be up to 3,660 m (12,000 ft) in length.When one or more third-party MS/TP device is connected on the FC bus, the device andbus segment limits are as follows: Each bus segment can be up to 1,220 m (4,000 ft) in length. Each FC bus can be up to 3,660 m (12,000 ft) in length.Note: Do not place subordinate devices on the FC bus. Subordinate devices on theFC bus are not supported.When using fiber-optic connections: 2,010 m (6,600 ft) between two fiber modems.22 AWG Stranded, 3-Wire Twisted, Shielded CableThe EOL switch must be set to On (or an EOL terminator installed) on the two deviceslocated at either end of each bus segment on an FC bus. The EOL switches must be set toOff (or EOL termination disabled) for all other devices on the bus segment on an FC bus.See End-of-Line Termination on Local FC Bus for more information.Notes: The recommended cable type provides the best bus performance. See MS/TP Bus CableRecommendations for information on alternative cable types and lengths that may be used inMS/TP applications. If third-party devices are connected to the bus, the cable lengths should be reduced (ifnecessary) to match the third-party vendor recommendations.14FX MS/TP Communications Bus Technical Bulletin

Figure 6: FC Bus with Three Bus Segments Connected with RepeatersThe bus segments on an FC bus are connected using repeaters (only). A repeater has two deviceconnections, which are independent of each other. Each device connection on the repeater isconnected to a bus segment just like any other device connection on the segment, and a repeaterdevice connection can be connected at the end of a bus segment or anywhere along the segment.When a repeater device connection is at the end of a bus segment, EOL termination must beenabled on that repeater device connection. See Figure 7 for more examples of repeaters on FCbuses.Table 4: FC Bus SpecificationsCategoryError CheckingDevice AddressingData Transmission StandardSignaling MethodSignaling RateTransient ImmunityEOL Termination MethodSpecificationMessage Headers checked using 8-bit Cyclic Redundancy Check (CRC) test.Message data check using 16-bit CRC test.0–255 (See Device Addressing on the MS/TP Bus for more information.)RS485

On an SA bus, a CGM, CVM, SNC, or FX-PC controller is the bus supervisor. The SA bus is a private MS/TP bus that only supports those devices that can be defined using the Controller Configuration Tool (CCT) programming tool. The bus does not support bus segments (Figure 10). See SA Bus Rules and Specifications for more information.