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FAQ (Frequently Asked Questions)
DP Base Programming Interface for CP 5613/CP 5614
C79000-G8976-C108-01
211
5.3 FAQ Check List for Programmers
What are the most important aspects of the program structure?
Make sure that you keep to the rules below when structuring your program:
x
Begin your user program with a DP_start_cp, DP_open and DP_get_pointer
and always complete these with DP_release_pointer, DP_close and
DP_reset_cp.
x
Evaluate all errors and check all the diagnostic data.
x
Check that all the conditions necessary for validating the data are met (for
example, when reading slave data, the master must be in the OPERATE or
CLEAR mode and the slave in the READY state).
x
Read out alarms with DP_read_alarm and acknowledge them with
DP_alarm_ack.
x
Events can be reported in any order; so make sure that your algorithms are
suitably flexible.
x
Do not send more than one asynchronous DPC1 job to a slave at the same time
(DP_ds_read/DP_ds_write, DP_alarm_ack).
x
If the result of a DP_enable_event call has been fetched, it must be sent again.
Should I retain the pointer while my program is running?
As long as your user program is in possession of the pointer to the process image
(DP_get_pointer call), no other user program can access it. In this case, retain the
pointer until the end of the program. If you only access the process image
sporadically, for example, as a diagnostic program or when you do not have real-
time requirements, you should release the pointer after every access or cycle.
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