Difference between revisions of "BACnet MS/TP"

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[[NSDU]]max = max ( [[APDU]], [[RPDU]] ), and Prior to Revision ** (prior to 135-2006), was 480 bytes.  
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[[NSDU]]max = max ( [[APDU]]ms/tp, [[RPDU]] ), and Prior to Revision ** (prior to 135-2006), was 480 bytes.  
  
 
[[NPCI]]max = 9 + 6 byte MAC + 7 byte MAC = 22
 
[[NPCI]]max = 9 + 6 byte MAC + 7 byte MAC = 22

Revision as of 11:52, 12 November 2018

BACnet "Master-Slave/Token-Passing" is the optional, RS-485 based physical layer for BACnet. It is based on cheap, relatively slow, serial communications.


Starting with Addendum 135-2008ab, 9600 and 38400 are the required baud rates and all of the others (19200, 57600, 76800, and 115200) are optional


MS/TP Frame Format
0x55 Framing 1
0xFF Framing 2
Frame Type
Dest MAC
Src MAC
Len MSByte
Len LSByte
Header CRC
Data This is the NPDU, if len non-zero
Data CRC MSByte if len non-zero
Data CRC LSByte if len non-zero


NSDUmax = max ( APDUms/tp, RPDU ), and Prior to Revision ** (prior to 135-2006), was 480 bytes.

NPCImax = 9 + 6 byte MAC + 7 byte MAC = 22

So NPDUmax = NSDUmax + NPCImax = 480 + 22 = 502

And so MPDU = NPDUmax + 10 (above) = 512




Keyword List
APDU BBMD BVLC BVLL DADR DNET Encoding I-Am LSAP MAC NPCI NPDU NSAP NSDU SA SADR SNET

Device Profiles

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Glossary