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S5-115F Manual
2.2.2
Program Scanning
The input signals to the input modules are scanned cyclically before program scanning and
mapped in the PII. The control program processes this information along with the current flag,
timer, and counter data. The control program consists of a sequence of individual statements. The
processor fetches the control program from the program memory and processes it statement by
statement.
The results are written to the PIQ. After the processor scans the program, it transfers the PIQ data
to the output modules.
The operating system of the S5-115F executes the following additional functions when addressing
double-channel I/O modules:
•
Digital inputs
•
Digital outputs
•
Analog inputs
Even during cyclic program scanning, quick response to signal changes is possible using the
following methods:
•
Using operations with direct I/O acces (e.g. L PB, T PB).
•
Programming multiple direct I/O scans in the control program.
•
Programming organization blocks to handle interrupts.
The processor starts a monitoring time every time program scanning starts (scan trigger). If the
scan trigger is not restarted within the configured scan time, e.g. because the control program
contains an infinite loop or there is a malfunction in the CPU, the PC goes into the "STOP" mode
and disables all output modules. Figure 2-3 shows a schematic representation of cyclic program
scanning.
Figure 2-3. Schematic Representation of Cyclic Program Scanning
EWA 4NEB 811 6148-02
- Read in
- Exchange and comparison
- Discrepancy analysis (differentiation between long-term and short-
term signal discrepancies with uniform input signal generation)
- Exchange and comparison of I/O images
- Output
- Read in
- Exchange and comparison
- Discrepancy analysis (differentiation between permissible and im-
permissible discrepancies between both analog values and between
short-term and long-term impermissible discrepancies)
RESTART
Start the
monitoring time
Update the PII
Scan the
control
program
Transfer the PIQ
Technical Description
2-5
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