Introduction to STEP 5
S5-100U
7.4.3
Cyclic Program Processing
Figure 7-13. Cyclic Program Processing
The operating system calls OB1 cyclically. If you want to
have structured programming, you should program only jump
operations (block calls) in OB1. The blocks you call up, PBs,
FBs, and SBs, should contain completed functional units in
order to provide a clearer overview.
A time monitor is triggered at the beginning of each program
processing cycle (scan cycle trigger). If the scan cycle time
trigger is not reset within the scan monitoring time, the CPU
automatically enters the STOP mode and disables the output
modules.
You can set the monitoring time (see Table 6-6). You could
have a control program that is so complex that it cannot be
processed within 300 ms. With CPU 103 and higher, you can
use OB31 (see section 9.3) to lengthen (retrigger) the scan
monitoring time in the control program.
Monitoring time is exceeded, for example, if you program
endless loops or if there is a malfunction in the programmable
controller.
Cycle trigger
Transfer
data
Control
program
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Содержание SIMATIC S5-100U
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Страница 531: ...E Reference Materials EWA 4NEB 812 6120 02b ...
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