Scan Cycle Load from Communication

Using the parameter "Scan cycle load from communication" you can control the duration of communication processes which always extend the scan cycle time so it does not exceed a specified length. Communication processes can be, for example, data transmission to another CPU via the MP or loading blocks (triggered by means of a programming device).

Test functions with the programming device are hardly affected by this parameter and may greatly extend the scan cycle time. The time available for test functions can be limited in process operation (S7-300 only). 

How the Parameter Works

The operating system of the CPU continuously provides the communication process with the configured percentage of the total CPU processing capacity (time slice technology). If this processing capacity is not needed for the communication, it is available to the rest of the processing.

step7的手册里有这个介绍。

cpu的 cycle /clock memory中， 有个参数Scan Cycle Load from Communication。 

貌似317和400的才有， 就是通讯的 cpu时间片占比。