Hello

Yesterday our S7-414 went into stop. The only message in the diagnostic buffer was : STOP caused by PG stop operation or bySFB 20 

The last message before was from some days earlier

When this happend we couldn't start the cpu again. When starting from the software or by switching the cpu to stop and run. Even switching power off and on the cpu didn't went to running mode.

Eventually we reset the cpu, and downloaded the program. After this the cpu went back in run.

Has anyone an idea what this problem caused?

Hello,

only idea (I'm not expert on 400 system) is check OBs existed and inside code for some specific operation. Next as general is check CPU options (cfg) for all parameters for sure to not allow some other possibilities.

Hi!

If you did not stopped the CPU by PG , then you can search your program to see what triggered the stop.

System Software for S7-300/400 System and Standard Functions Volume 1 and Volume 2.

Up here you can read more about system functions/function blocks. If SFB20 is programmed, then a rising edge at REQ input will put the CPU in STOP. SFB 20 is "Changing a Remote device to stop state". 

Have a read and check your program. Also check other threads already in the forum regarding the issue.

Hope it helps, Mihai.