CMND Instruction Unit Error / CPU Bus Error

What does 25-05 mean?

This error indicates a problem with the communication unit itself or the CPU bus, preventing the CMND instruction from executing properly. This is often a hardware or configuration issue with the serial communication unit (SCU), affecting its ability to communicate with the PLC CPU.

• Faulty Serial Communication Unit (SCU) hardware.
• Improper installation or seating of the SCU module on the CPU bus.
• Configuration errors in the SCU's initial settings or I/O memory allocations.
• Electrical noise or interference on the CPU bus affecting SCU communication.

Click steps to track your progress.

1. 1

   Verify the SCU module is correctly inserted and secured in its slot on the CPU rack, ensuring all connectors are fully seated.

2. 2

   Check the SCU's initial settings and I/O memory allocations as per '2-3-2. CIO Area' in the CJ Series Serial Communications Units OPERATION MANUAL (Cat. No. W336).

3. 3

   Inspect the CPU bus connectors for any physical damage, corrosion, or debris.

4. 4

   Perform a power cycle of the PLC system by turning off and then on the main power supply to reset the SCU module and CPU bus communication.