I would like to know why the PLC manufactures (At least few) are giving warning to keep the PLC power on while upgrading the firmware? Why PLC is become useless if power goes of while upgrading the firmware?

Is all brand PLC are having the similar issues?
How PLC firmware upgrade is happening?

 

Dear Denson,

Because while you are doing the firmware upgrade process, you are ripping the current firmware stored on the flash memory and replace with new firmware. If you are loosing power when the process is not complete, your old firmware is ripped in the half and not replaced completely with new firmware, means half of flash memory will be storing uncomplete old firmware and the other half will containing uncomplete new firmware, so this will become useless firmware. This is the same case like you are loosing your PC or LAPTOP loosing BIOS or loosing hard drive containing OS.

Since the firmware is not complete now , when you turn the power back, CPU will boot and try to read firmware from flash memory location but the firmware now is not complete (or damage) the CPU will not be able to starting up her operating system and the CPU become useless brick now.

As long as my knowledge , all of PLC brand (Major brand like Rockwell and Schneider) will have the same situation when the same happen.

 

If this the reason, how are ABB drives firmware upgrade is working. I could see what ever happens while upgrading the ABB drives, they were able to reload it again. Even in power failure cases it fails the firmware upgrade but user can reload it again.