Be farmiliar with Modicon M580 hot standby LED sequence during power cycle. Throughout my profesional career, I have had been asked ever time about what does the Modicon M580 CPU LED sequence looks like when power is lost in one of the CPU. I figured to put this to rest once an for all, I am creating this video.

Couple of pointers to take away.

  • The Primary (active) PLC will have a solid green LED on (PRIM) when the PLC is the Primary PLC.
  • The STBY (standby) LED will be blinking every 1/2 second on the Primary PLC when the it cannot connect to the Standby PLC.
  • If the Primary PLC detects (connects) to the standby PLC, the STBY LED on the Primary PLC will be off. The image below illustrates PLC A is the Primary PLC. Note that the STBY LED is off.
    Xybernetics PLC A is the Primary PLC
  • If a PLC is on Standby, the STBY LED will be solid green. Dee image below.
    Xybernetics STBY LED will be solid green If PLC in Standby
  • Speed of PLC going to Standby mode. In this video, you can see that PLC B takes about 40 seconds to normalize (enter standby mode) while PLC A take about 100 seconds. Both PLCs have the same firmware version. If you know why, please leave a comment so that your contribution can be shared with everyone.
  • You cannot have both PLCs (A and B) with PRIM LED light. This is due to the rotary dail (at the back of the CPU) not assigned/setup correctly. Power cycle will be required to set this up.
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About the
I am a software developer in Calgary, Alberta, Canada with passion in getting my fingers in any new technology. I started software development when I was 10 years old and have never looked back. Now with well over 35 years of software development, I wanted to share some of these key knowledge with the people of the world in the wide web.