Transcription of BACnet MS/TP - kargs.net
1 1 BACnet MS/TP Physical and Electrical considerations Packet structure Receive Frame State Machine Slave and Master Node State Machine Design issues (timing, buffering, MAC address) 2 BACnet MS/TP EIA-48512012051047K47K+5 RTSTxRx510+5 RTSTxRxRTSTxRx+++---Node with networkbias resistorsNode with localbias resistorsNode withoutbias resistorsBaud Rates: 9600, 19200, 38400, 57600, 76800 Parity: noStart Bits: 1 Stop Bits: 1 Least Significant Bit First (same as EIA-232)Uses standard UARTThis may not be the ideal circuit for EIA-485. There has been much debate in the BACnet MS/TP working group about it. 3MS/TP Packet Structure0x55 Preamble0xFFLengthDestination AddressSource AddressFrame TypeHeader CRCDataData CRCpad2 octets, most significant octet first1 octet1 octet1 octet2 octets1 octet(present if Length is non-zero) Length octets(present if Length is non-zero) 2 octets(optional)
2 At most, 1 octet0xFF 4 Receive Frame State MachineIDLEDATACRCBad CRCGood CRCEatAnOctetEatAnErrorPreamble 1 TimeoutNotPreamblePREAMBLEE rrorHEADERCRCBadCRCNoDataNotForUsHEADERF rame TypeDestinationSourceLength 1 Length 2 DATAP reamble 2 CRC 1 Data OctetDataTimeoutErrorHeaderCRCT imeoutErrorRepeatedPreamble 1 CRC2 FrameTooLong 5 Master Node State MachinePOLLFORMASTERDONEWITHTOKENINITIAL IZEUSETOKENPASSTOKENWAITFORREPLYIDLENOTO KENANSWERDATAREQUESTSendMaintenancePFMN othingToSendSendNoWaitSendAnotherFrameSo leMasterSoleMasterDeclareSoleMasterSendN extPFMSendAndWaitReceivedReplyReplyTimeO utInvalidFrameReceivedPostponeSendTokenR esetMaintenancePFMR eceivedReplyToPFMDoneWithPFMFindNewSucce ssorGenerateTokenSawFrameLostTokenReceiv edUnexpectedFrameRetrySendTokenSawTokenU serReceivedUnexpectedFrameReceivedTokenD eferredReplyReplyReceivedDataNeedingRepl yDoneInitializingReceivedPFMR eceivedDataNoReplyReceivedInvalidFrameRe ceivedUnwantedFrameSoleMasterRestartMain tenancePFM 6 Slave Node State MachineINITIALIZEDone InitializingANSWERDATAREQUESTR eceivedDataNeedingReplyReplyCannot ReplyReceivedUnwantedFrameReceivedInvali dFrameReceivedDataNoReplyIDLE 7MS/TP TimingTframe_abort< 60 bit times55FF00720A0000A955FF00037200009555FF00A003000004 Tturnaround> 40 bit timesTusage_timeout< 20msTokenTokenTokenTpostdrive< 15 bit times 8MS/TP Timing55FF01070300006D55FF000A03000004 TokenPoll For MasterTusage_timeout< 20msEF0F412D55FF00720A0000A9 Treply_timeout< 255msToken8000010E310062FF010402055307C4 0255FF05890A001212
3 BACnet Data Expecting Reply 9 BACnet Data Expecting Reply May use Reply Postponed Practical use only in RTOS or queued data Single buffer, single thread, just reply Buffer, queue - match packet signature 10MS/TP MAC Address Master Node MAC 0-127 (0x00 - 0x7F) Slave Node MAC 0-254 (0x00-0xFE) Broadcast 255 (0xFF) DIP switch, dials, LCD Non-volatile, same after power cycle or reset Proposed Auto Addressing (DHCP, ZeroConfig)
