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Controller 450 User’s Guide
Section 4.1.10 Execution
3BSE 002 415R701 Rev A 4-23
4.1.10.2 Execution Sequence within an Execution Unit
When the cycle time and the start conditions for an execution unit are satisfied, the following
takes place:
• All input data stored in the data base for the PC element included in the execution unit is
read into the local data area.
To get close synchronization between I/O scanning and PC execution a common
interpreter is used. See Section 4.1.10.7, Scanning of Process Inputs.
• The program codes of the PC element within the execution unit are executed.
• Data from the local data area is read out to the data base for the output variables which
store their values in the data base.
4.1.10.3 Sequence of Execution of Execution Units
In certain applications, the order in which execution units are executed is of interest. Assume
that a function is divided into execution units which exchange data with each other and that
these units have the same cycle time, see Figure 4-15.
It is also assumed that execution unit 1 is required to execute before unit 2.
When the conditions for an execution unit are defined, it is possible, with the call parameter
“Place in the cycle table,” to specify a place number between 1 and 255. This place number
specifies the order in which the execution units are executed during the same cycle time.
If, in the example, the place number 1 is specified for the execution unit 1 and the place number
2 is specified for unit 2, the required function is obtained.
The different execution units may well belong to different PC programs, but they must all have
the same cycle time. For units with different cycle times, there is no defined sequence.
A required start sequence can, however, be obtained by controlling the start conditions for the
execution units included.
Figure 4-15. Function consisting of two Execution Units
CONTRM
50ms
Execution unit 1
CONTRM
50ms
Execution unit 2
Data
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