Siemens SIMATIC MV550 S Operating Instructions Manual page 128

Process interfacing via an automation system (PLC, PC)
9.4 Control with FB 79
Note
Reading and processing analogous to the time diagrams
Writing the control byte and reading and evaluating the status byte must be performed in the
same way as in the time diagrams shown under "Select program".
"Send/Receive" user data interface
Table 9- 35
Byte
0
1
2
3
4
5
...
31
Note
Coding of the sent data
The "4 Data ID of the supplied data" byte defines the transferred data. The coding matches
byte 4 of the "Receive" user data interface. With a read job on the "Receive" user data
interface, the ID of the data currently being transferred is entered here.
Table 9- 36
Byte
0
1
2
3
4
5
...
31
128
Send
Description
Reserved
Consecutive number of the data packet to be transferred to the I/O controller.
Total net length of the data to be transferred in bytes in STEP 7 format.
--
Data ID of the supplied data
1st user data byte
...
27th user data byte
Receive
Description
Reserved
Consecutive number of the current data packet received correctly by the I/O controller
Reserved
Reserved
Data ID of the requested data
Reserved
...
Reserved
Operating Instructions, 05/2019, C79000-G8976-C494-02
SIMATIC MV500