S7-400 CPU went to stop operating mode

Hello Experts,

The plant is running for 2 years already. Recently our CPU-416-3 PN/DP incorporate with some scalance x-200 series using fiber optics goes to stop operating mode and SF enable. As check in the diagnostic buffer (event 9 see below), found that the date is changing then "Cycle time exceeded" error. Attached is the CPU Diagnostic Buffer.

Event 9 of 120:  Event ID 16# 3501
Cycle time exceeded
Run time of the last cycle (ms):      801
Cause: Current OB1 start event initiated by end of OB1 (free cycle)
Causing OB: Cyclic program (OB1)
Causing priority class:  1
Requested OB: Timing error OB (OB80)
Priority class: 26
Internal error, Incoming event
10:20:33.702 AM  01/10/2019
(Coding: 16# 3501  1A50  C358  0321  1103  0101)

Can anybody share what causes this problem?

Regards,

Rem

Hello!

A little late maybe, but there are a few cases that can cause this error.  

The most common one is an endless loop. 

You mentioned that you installed a new hardware and maybe there was some new software also? 

Quote from another post:

 "The PLC needs to run through all the code before a certain time period. If it does not do so, it will cause such a stop. This is to prevent the system to be crippled by endless loops."

Poor programming can cause such an error, especially STL written loops or poor indirect addressing.

You can have a look at this thread.

Regards, NastasaM