Example: PCMM2G Heavily Loaded CPU

This example shows an application that is heavily loading a PCMM2G with the EtherCAT Cycle Time = 250 microseconds.

Specifically, this example looks at:

1. MotionExec and PLCProgExec Times

Using the techniques described in Practical Application: Using Trace Time To Measure CPU Load, examine the MotionExec and PLCProgExec times:

Figure 1: MotionExec and PLCProgExec Times

  • The average MotionExec = 20 microseconds.
    • This is about 8% (20 / 250) of the cycle time.
  • The average PLCProgExec = 178 microseconds.
    • This is about 71% (178 / 250) of the cycle time.
  • Thus, the PLC programs have a much higher load.

2. PLCProgExec Peaks

Figure 2: PLCProgExec Peaks

This shows there is not much time left over:

  • PLCProgExec = 212.

3. PLCMarginTime

Figure 3: PLCMarginTime

  • The PLCMarginTime is between 0 and 25 microseconds (0% to 10%).
  • This is not a comfortable margin for deterministic PLC performance.

4. Controller Log

The Controller log confirms the occasionally missing PLC execution cycles:

Figure 4: Controller Log

See Also