Example: PCMM2G Over Loaded CPU

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

Specifically, this example looks at:

• 1. MotionExec and PLCProgExec Times
• 2. RealTimeMargin
• 3. Controller Log

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 = 235 microseconds.
  • This is about 94% (235 / 250) of the cycle time.

2. RealTimeMargin

Figure 2: RealTimeMargin

• The PLCMarginTime is zero.
• There is not enough time to complete the PLC programs every cycle.

3. Controller Log

The Controller log confirms the missing PLC execution cycles:

Figure 3: Controller log

• The PCMM2G controller CPU core has plenty of time to execute the Motion Engine and Axes.
  • However, the CPU core running the PLC cannot complete within one Motion/EtherCAT cycle.
• The PLC programs are spanning multiple Motion/EtherCAT cycles.
  • This may cause trouble for application programs that rely on Motion and EtherCAT data updated every PLC cycle.

See Also

• Example: AKD PDMM and PCMM Heavily Loaded CPU
• Example: AKD PDMM and PCMM Over Loaded CPU
• Example: PCMM2G Heavily Loaded CPU