Hi,

How is it possible to read the CPU fault bit in TSX3721 Modicon PLC (or any other PLC) if the CPU itself is not working? How do I read the bit which stores the CPU fault information once the CPU is not working. Does the Communication card work irrespective the CPU is in fault or not.

Please, if anyone can sort this out for me.
Thanking you in advance.

Regards,
Parvez

 

Sometimes it does. Most of the time when a PLC faults, the processor has not even really failed. I dont think I've ever seen a processor actually fail, so i dont have first hand experience. But i know that some PLCs have separate chips that run the communications, and the holding registers are separate from the processor, so i would think that normally, it wouldnt be too much of a problem getting the fault code. Course, in those cases the fault code is not likely to be helpful, I'm sure the best you will get is 'processor broken' or something. Maybe you might get a 'duh' out of it (I have seen those, its called kernel mode)

-jeff