Error in MSG intruction in Modbus RTU network

JDFP

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Feb 2020
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San Cristobal
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Hello, friends. I have a Micrologix 1100 connected to a Schneider ATV312 drive through Modbus RTU. My intention is to control the frequency of the motor through the modbus conection, and start it using the drive built-in keypad.

I configured all the parameters in order to do this and I made it, I controled the frequency of the drive and can start de motor through the keypad, but despite I made this, the error flag of my MSG instructiong gets triggered with time out error.

I made just a simple ladder logic that send frequency value to the modbus register using a bit, and reset my instruction after a determined time if an error is detected. But do not understand why the error flag of MSG gets triggered if communication has been done (I can see the frequency value in drive built-in screen).
 
What is the error message that you are getting?
I would ensure that you are sending the MSG only once. (One-Shot)
Since you are using Modbus RTU this is a serial communication method. Check to ensure that your communication wire is separate from your power lines. You could be picking up some noise. You can also try reducing the transmission rate.
Just some thoughts.
Regards,
 
Thanks for the replay.

1. The error code is "Message timed out in local processor" (37).

2. Yes, I send it only once.

3. The communication cables are sepparate from power lines

4. I have the baud rate in 19200. You think I should lower it?
 
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Are you sure that you have the right Tx and Rx connections? I keep some null modem adapters handy so I can plug one in to swap those lines for trials. Are you sure that you have the right number of data bits, stop bits and parity?

Are you sure about the Modbus addresses and data type? There can be devices that specify Input registers rather than Holding registers, 0 and 1 based addressing, and data type conflicts.
 
I'm sure of all thouse configurations. I was experiencing the problem yesterday, but when I tried today, with out no change, the MSG instruction does not give me any error. Thanks to all for your reply.
 
Most devices require a power cycle after making a change to a serial port setting. I know the Micrologix does. It normally gives a different error if you change protocols and fail to cycle power. Most VFDs I have worked with are similar in that they require a power cycle to accept a new Modbus address or certain other changes to the port settings.
 
If you’re only sending a single message, you should still at least determine whether the message is already working: a simple rung condition of “ XIO TheMessage.EN” will prevent triggering the message while it’s already active. This in turn can be preceded by your trigger logic on the same rung.
 
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