PROFIBUS Manual
The two address bytes in the telegram header of telegrams (Request, Confirmation and Response telegrams) contain the station's destination address (DA) and source address (SA).
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
DA: Destination address |
|
0 - 127 (0x7F) |
Destination address |
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0 1 |
|
|
|
|
|
|
|
no DSAP (SAP = NIL) DSAP present |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
SA : Source address |
|
0 – 126 (0x7E) |
Source address |
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0 1 |
|
|
|
|
|
|
|
no SSAP (SAP = NIL) SSAP present |
Address 127 is reserved as a global address for broadcast or multicast messages (telegrams to all bus users or user groups selected via service access point; only allowed with Send Data with No Acknowledge, SDN).
The address byte of the Request telegram should be reflected in the Response telegram in reverse, i.e. the SA byte of the Response telegram contains the destination station address and the DA byte the source station address of the Request.
For formats with a PDU, the address extension serves to identify a destination and/or source address extension in the form of a Service Access Point (SAP) that immediately follows the FC byte in the PDU. The address extensions of a Request telegram must be reflected in the Response telegram in reverse.
If the address extension bit has not been set, it is the special SAP = NIL. This Service Access Point has the advantage that its telegram is 2 bytes shorter and is therefore used for cyclic data exchange.
