Tag Number
From BACnet Wiki
There are two types of Tags, and the Tag Number usage varies with each.
- Application Tags
- These have fixed type - boolean, int, date etc.
- Context Specific Tags
- The types of these tags depend on where they are found, in the variable part of the APDU. Their type cannot be determined by inspection alone.
- They have an associated context number; this context number specifies the meaning of the data.
- Context Tags also allow Constructed Tags (lists) to be created.
- See section 20.2.1, pg 377 of the specification
Another resource is | BAC Cave, from BACnet Bill]
| Octets | Meaning | |||||||
| 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 | |
| 1 | Tag Number | Class | Length/Value/Type | |||||
| n | Variable amount of data | |||||||
Class = 0 for Application Tags (will indicate the Type of tag)
Class = 1 for Context Specific Tags (Will indicate the sequence of the tag)
| APDU BBMD BVLC BVLL DADR DNET Encoding I-Am LSAP MAC NPCI NPDU NSAP NSDU SA SADR SNET |
| Edit this box. |
