Siemens SIMATIC ET 200AL System Manual page 179

Interrupts, error messages, diagnostics and system alarms
5.3 Alarms
5.3.2 Slave diagnostics
The figure below shows the structure of the slave diagnostics.
Figure 5-11
Note
The length of the diagnostics frame varies with the IM 157-1 DP (depending on parameter
assignment) between 6 and 244 bytes in DPV1 mode.
You can identify the length of the last received diagnostics frame in STEP 7 from the
RET_VAL parameter in SFC 13.
36
Structure of the slave diagnostics
Interface module IM 157-1 DP (6ES7157-1AA00-0AB0)
Manual, 12/2016, A5E32100641-AD