Modbus over Micrologix 1400 B series

sinusterror · Oct 3, 2017

Hello people!, I finally was able to get the job done with modbus in my AB ML 1400, now my question is, I´m receiving correctly the information from modbus TCP to my MSG table in RSLOGIX, but when the data that I´m reading suddenly change, the data doesnt change in my MSG table unless i reboot the AB unit, any clues?

OkiePC · Oct 3, 2017

Is the Micrologix initiating the communication? Can you post the logic (zip it first)?

sinusterror · Oct 3, 2017

Hello OkiePC, acutally my logic isnt pretty much developed, I´m just testing the MODBUS, its only a input bit NC, that is activating a MSG, the thing is that I´m sending updated values with my arduino with MODBUS, and only rebooting the PLC will update the table.

OkiePC · Oct 3, 2017

sinusterror said:
Hello OkiePC, acutally my logic isnt pretty much developed, I´m just testing the MODBUS, its only a input bit NC, that is activating a MSG, the thing is that I´m sending updated values with my arduino with MODBUS, and only rebooting the PLC will update the table.

This is a guess, but it sounds like your MSG instruction is only happening once each time the PLC goes to run mode. You need logic to cause the MSG to repeat.

sinusterror · Oct 3, 2017

mmm, I thought the loop of the ladder itself might do the magic, but seems I´m wrong, do you have an basic example of how to keep a MSG alive all the time OkiePC? in advance thank you very much for the support.

OkiePC · Oct 3, 2017

I normally monitor the ER and DN bits from the message instruction to know that it either completed or failed and then move on to the next message.

It is often useful to have some delay between each message. You don't want to overwhelm the port with requests.

So in your case, you could do something like this. I didn't test this logic, just whipped it out real quick, so there could be a mistake:

sinusterror · Oct 3, 2017

worked like a charm okiePC!! you´re the best!!! thank for the super support!

Modbus over Micrologix 1400 B series

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