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M91-2-R1 communication error

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If you go into information mode for the PLC you can get into system settings and go into the system section you should be able to make a PLC change from run to stop or the other way around.  However I have never encountered a program where the act of running the program stopped the PC communications, however first time for everything.  If you stop the PLC and are able to communicate then the program is what caused your problem.


Good Luck


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  • MVP 2023

The only way to stop the program, that I know of, is through the Information Mode or by command from a PC that is online with the PLC. The one exception would be if the Watchdog timer were to expire. Another possibility would be if the PLC battery is bad and there was a power failure (I think you only lose RAM values in the M91, not the program [not sure off the top of my head], but that may be enough to cause your problem).


From a hardware standpoint, other than the battery, the RS232 serial port may have had a failure - or a failure in the connection between the PC and PLC. If you're using a GSM modem to communicate, there are a number of other possibilities to investigate.

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  • 4 years later...

Hi i not speak english very good , but i trie my problem is  i want to buy  a m91-2r1  with a io -pt 4 an a module ex a1 can i with this instrument work with rtd 3000 or is only for pt-100 and pt-1000? and with only this i can make a proyect  for mintoring a 4 temperature ?do not i nesesite a software aditional or another hardware or is better to buy a anlaogic input module please help me in what i need ?

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