Difference between revisions of "BACnet MS/TP"

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Line 23: Line 23:
 
|Header CRC ||  
 
|Header CRC ||  
 
|-
 
|-
|Data || if len non-zero
+
|Data || This is the [[NPDU]], if len non-zero
 
|-
 
|-
 
| Data CRC MSByte || if len non-zero
 
| Data CRC MSByte || if len non-zero
Line 35: Line 35:
 
[[NPCI]]max = 9 + 6 byte MAC + 7 byte MAC = 22
 
[[NPCI]]max = 9 + 6 byte MAC + 7 byte MAC = 22
  
So [[NSDU]]max = 480 + 22 = 502
+
So [[NPDU]]max = 480 + 22 = 502
  
And NSDUmax + 10 (above) = 512
+
And so [[MPDU]] = [[NPDU]]max + 10 (above) = 512
  
  

Revision as of 12:49, 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


Prior to Revision ** (prior to 135-2006) Max APDU was 480 bytes.

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

So NPDUmax = 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