Running a program while PLC in stop

In S5-155U, OB39 is processed during the so-called "smooth stop".

I always assumed there a counterpart of OB39 in S7, but to my surprise couldn't find any. Probably because S7 CPU's are much more sophisticated and you can trigger a special OB processing during almost any situation and prevent the CPU from going to stop (unless there is a total HW failure).

If the cyclic program is interrupted causing a change to the SOFT

If the interruption of the cyclic program means that a handling block

(communication) is not completely executed, it is possible and

permitted to re-call the same block or the same block type in OB 39

(e.g. SEND).

STOP Mode

The execution time of OB 39 is monitored by the system program. If

execution takes longer than 2.55 seconds (fixed value), the system

program detects a cycle time error; it then calls the error OB, OB 26,

and then processes OB 39 again from the beginning. If a cycle time

error occurs again, an ISTACK depth > 5 causes an ISTACK overflow

(reaction: see following paragraph).



in this context, the S7 mantain actives his S7 funciton (as server) while CPU in STOP. So, maybe, that makes no sense to have a "OB39" in S7.