先把倒数第二个问题的答案公布一下：
其实在任何一个400CP卡手册中都有如下说明：
8.6 Recommendations for use with a high communications load
Overview
When using the CP described here, the points below will help you to avoid overload situations on your CPU.
In particular when you replace an older CP with the CP described here and are then confronted with overload problems, you should check your application for the pitfalls outlined below.
Known problems
1. The functions for sending and receiving (FC5/FC6, FC50/60 or FC53/63) are often called cyclically in OB1. This leads to constant communication between the CPU and CP. As a result, other types of communication such as PG functions cannot be executed or only very slowly.
2.HMI systems access data of the CPU too often using S7 functions. This slows down communication generally and can lead to lack of resources on the CPU if SEND/RECEIVE FCs are called in OB1 cyclically (effect: reduced data throughput or increased reaction time).
Remedy
The recommendations below will help to avoid these situations:
1， Do not call communication blocks cyclically in OB1!
Communication should be called time-controlled in a suitable cyclic-interrupt OB. The call interval of this OB should be significantly higher than the average cycle time of OB1.
2, You should set a minimum cycle time that is higher than the average runtime of OB1. This frees resources for communication on the CPU. This is, for example,a remedy for existing applications when communication already takes place cyclically in OB1.
3, If necessary, reduce the time taken for communication processing on the CPU by changing the parameters set for “cyclic load due to communication”in the properties dialog of the CPU.
在家做试验很难，不过现场到碰见好几次。


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