Siemens SIMATIC S5-100U System Manual page 33

S5-100U
Data Cycle
Prior to a program scan, the external I/O bus transfers current information from the input modules to
the process image input table (PII). At the same time, information contained in the process image
output table (PIQ) is transferred to the output modules.
Data cycle
Shift
data
Interrupt Data Cycle, for CPU 103 version 8MA02 and higher
There is an interrupt input data cycle prior to each time-controlled or interrupt-driven program scan.
Before a time-controlled program scan, current information about the input modules is read into the
interrupt PII. Before an interrupt-driven program scan, interrupt inputs on slots 0 and 1 only are read
into the interrupt PII.
Following a time-controlled program scan, there is not an interrupt output data cycle until data has
been moved into the interrupt PIQ via a transfer operation (see section 6.6.2).
Information is output from the interrupt PIQ to the output modules during an interrupt output data
cycle. The PIQ is updated.
EWA 4NEB 812 6120-02b
Program scanning
Transfer data from the shift register to
the output modules.
Load data from the input
modules into the shift register.
Figure 2-6. Data Cycle
Technical Description
Shift
data
Time axis
2-7