Cyclic Program Execution In The S7-200 Plc - Siemens SIMATIC S7-200 Manual

Cyclic Program Execution in the S7-200 PLC

0 1 2
STEP 7 program,
- Bit memories
- Timers
- Counters
- ...
0 1 2
All SIMATIC PLCs operate cyclically. During each cycle, the switch states are first read in from the
inputs, and then stored in the process-image input table. The control program is then executed on the
basis of this information.
The outputs in the process-image output table are subsequently controlled in accordance with the
circuit logic of the program. The last step is to transfer the states from the process-image output table
to the physical outputs. The cycle is then repeated.
Hardware Software
Begin of cycle
Process-image input table
Process image output table
End of cycle
Basic
Settings
Inputs
Outputs
1st Exercise More
Program Exercises
n
n
Appendix
50