Technical data

Diagnostics
23.7 Checking Scan Cycle Times to Avoid Time Errors
Programming with STEP 7
494 Manual, 05/2010, A5E02789666-01
23.7 Checking Scan Cycle Times to Avoid Time Errors
23.7.1 Checking Scan Cycle Times to Avoid Time Errors
The "Scan Cycle Time" tab in the module information gives information about the scan cycle times
of the user program.
If the duration of the longest cycle time is close to the configured maximum scan cycle time, there
is a danger that fluctuations in the cycle time might cause a time error. This can be avoided if you
extend the maximum cycle time (watchdog time) of the user program.
If the cycle length is less than the configured minimum scan time, the cycle is automatically
extended by the CPU/FM to the configured minimum cycle time. In the case of a CPU, the
background OB (OB90) is processed during this extended time (if it has been downloaded).
Setting the Scan Cycle Time
You can set the maximum and minimum cycle times when you configure the hardware. To do this,
double-click in the offline view of the configuration table on the CPU/FM to define its properties.
You can enter the appropriate values in the "Cycle/Clock Memory" tab.