Processing Times¶
Terms
The most important times for the use of the AC500 basic unit with or without connected remote modules are:
The reaction time is the time between a signal transition at the input terminal and the signal response at the output terminal.
For binary signals, the reaction time is composed of the input delay, the cycle time of the program execution and the bus transmission time if the system is expanded by remote modules.
The cycle time determines the time intervals after which the processor restarts the execution of the user program.
The cycle time has to be specified by the user. It should be greater than the program processing time of the user program plus the data transfer times and the related waiting times.
The cycle time is also the time base for some time-controlled functions.
The program processing time is the net time for processing the user program.
Program Processing Time
| Statements | PM55x-xP PM56x-xP |
PM57x | PM58x | PM59x |
|---|---|---|---|---|
| - Binary statements of the type: | ||||
!M /M &M =M !NM /NM &NM =NM !M /M &M =SM !NM /NM &NM =RM Processing time for 1 instruction: |
min. 0.08 µs | min. 0.06 µs | min. 0.05 µs | min. 0.002 µs |
| - Word statements of the type: | ||||
!MW +MW -MW =MW !-MW -MW +MW =-MW !MW *MW :MW =MW !-MW *-MW :-MW =-MW Processing time for 1 instruction: |
min. 0.1 µs | min. 0.09 µs | min. 0.06 µs | min. 0.004 µs |
| - Floating point: | ||||
| Processing time for 1 instruction: | min. 1.2 µs | min. 0.70 µs | min. 0.50 µs | min. 0.004 µs |
Set Cycle Time
It is assumed that the processor always gets access in a moment with a worst-case condition.
The cycle time is stored in the task configuration and can be selected in steps of 1 ms. If the selected cycle time is too short, the processor will not be able to completely process the tasks assigned to it every cycle. This will result in a time delay.
If this lack of time becomes too large over several cycles, the processor aborts the program execution and outputs an error (E2).
For some function blocks, such as the PID controller, the error-free execution depends on an exact timing sequence. Make sure that there is a larger time reserve.
To check the correct cycle time, perform the following steps:
- Load the user program into the basic unit.
- Check the capacity utilization with “Online/PLC Browser/cpuload”.
- Change the cycle time until the capacity utilization is below 80 %.
When setting the cycle time, consider the following values:
- Time for reading and copying the input signals from the I/O driver to the I/O image.
- Time for copying the input signals of the user task from the I/O image to the image memory.
- Program processing time.
- Time for copying the output signals of the user task from the image memory to the I/O image.
- Time for copying the output signals from the I/O image to the I/O driver and applying the I/Os to the I/O module.
- Receiving/sending interrupts from Communication Module telegrams within the cycle time.
- Receiving/sending interrupts from the serial interface within the cycle time.
- Task changes.
- Runtime of the watchdog task.