Siemens S7-300 用户手册

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SIMATIC S7-300 Getting Started for First Time Users
Getting Started, 04/2007, 6ZB5310-0NC02-0BA0
Setting the parameters of the CPU 312C
You can set numerous parameters for each of the modules. As an example, we 
will modify the retention behavior of the CPU 312C. 
1. Set the amount of retentive bit memory to “0”.
The retention behavior of the 
CPU 312C determines 
whether or not the values of 
internal memory bits are 
retained after a power failure 
or memory reset on the 
CPU 312C.
You can use the retention 
behavior to ensure that the 
motor does not start up in an 
uncontrolled manner after a 
power failure.