Siemens simatic et 200s Operating Instructions Manual page 255

Principle
What You Do
Provide the control interface with data depending on the
MODE.
Check the POS_ACK feedback bit is at 0
Switch the START control bit from 0 to 1
Switch the START control bit from 1 to 0
Only when POS_ACK=0 can you start a new MODE.
If you start when a MODE is running, the 1PosSSI/Analog takes on the new motion and executes a change of direction, if
necessary.
Figure 6-5
ET 200S Positioning
Operating Instructions, 05/2007, A5E00124871-04
Control and Feedback Signals with MODEs
6.6 Functions of the 1PosSSI/Analog
Response of the 1PosSSI/Analog
The 1PosSSI/Analog sets the feedback bit POS_ACK = 1
and POS_DONE = 0.
You can tell from this that the start has been detected by the
1PosSSI/Analog and when POS_ERR = 0, the MODE is
executed.
The MODE is not executed when POS_ERR = 1.
The 1PosSSI/Analog sets the feedback bit POS_ACK = 0
In the case of a stop, the reference point run, and absolute
and relative positioning, 1PosSSI/Analog sets the feedback
bit POS_DONE = 1 when the MODE is completed without
errors.
When POS_ERR = 1 the MODE is terminated with an error.
1PosSSI/Analog
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