The cycle time is the time the CPU needs for:
● Updating the process image inputs/outputs
● Executing the cyclic program
● All program parts and system activities interrupting this cycle
● Waiting for the minimum cycle time (if it is parameterized and is longer than the program
execution time)
The cycle time (T
cyc
) is not the same in each cycle because the processing times may vary.
Causes of this include:
● For example, different program runtimes:
– Program loops
– Conditional commands
– Conditional block calls
– Different program paths
● Lengthening due to interruptions, for example:
– Time-driven interrupt processing
– Event-driven interrupt processing
– Communication