OB1 scantime and online diag. functions

Testermax

Hello!
Will the change of Entries in the Diagnostic buffer to max (module information) in any way disturb the running of OB1?

UMENCHO

Diagnostic buffer is part from working memory of the CPU. Any changes there should to ensure that do not exceed the available amount of working memory in the CPU. Look for more details at Automation System S7-400 CPU Specifications (from 86th page)

QUESTION:
Does an S7 CPU go into STOP because of a cycle overload?

ANSWER:
When configuring the hardware you can set a cycle monitoring time (ms) in the CPU properties (double-click CPU in the Hardware Configuration.

Make sure that the cycle monitoring time is always greater than the maximum cycle time of the current user program. If the cycle monitoring time is exceeded, the CPU goes into the operating state "STOP". However, you have the possibility in an OB 80 of reacting once to this ("retrigger") and thus prevent the "STOP" state of the CPU. If the cycle time is exceeded a second time, then the CPU inevitably goes into "STOP". Without the OB80 the CPU goes immediately into the "STOP" state.

Possible causes for exceeding the cycle monitoring time:

• The quantified project scope is too great
• Too many blocks are being processed too quickly
• Additional communications processes that take a long time
• Bundling of alarm events
• Error in the CPU program

With the minimum cycle time you define for OB 1 the time intervals in which the CPU program is called. If the cycle time is shorter than the minimum cycle time specified, then the CPU processes the OB90 (background task) until the minimum cycle time is reached.