Sending ASCII commands on Micrologix 1400

[gumba00]

Hi,

I am trying to get Allen Bradley Micrologix 1400 to send ASCII commands over a RS-485 2 wire connection. I can get PuTTy to communicate just fine. The communication settings are
Channel 0
Modbus RTU Master
Baud 19200
Parity None
Stop bits 1
data bits 8
No handshake (485 network)

I have the 1763-NC01 (aka the RS-485 connverter) plugged into channel 0. I have A and B wired to the other device. I am using the AWT command. I have The ST10:0-ST13:0 with the commands in them and using R14:0-R17:0 for control. The AWTs send all of the characters with no errors.

I have tried switching the A & B wires to no effect. I am stuck and out of ideas to try. Any suggestions?

 

[Ken Roach]

Welcome to the Forum !

If you need to send and receive ASCII strings, set the port mode for ASCII, not for Modbus RTU Master.

RA allows the AWT to function even when the port is configured for one of the industrial protocols like Modbus or DF1. But the AWA or ARL or ARD instructions don't work because the industrial protocol is controlling the input buffer.

 

[Ken Roach]

1763-NC01 isn't an RS-485 'converter'; it's just a wire terminal breakout that connects the Data A, Data B, and Signal ground from the round Mini-DIN8 connector to a screw terminal set.

Also remember that RS-485 is never really '2 wires'. There is always a common voltage reference, even if that reference is literally the earth. Be sure to connect the Data Common terminal on the NC01 to something that is also referenced by your end device.

 

[gumba00]

Ken,

1 Thanks i have looked stuff up on here for years this is the first time I have not found my solution already mentioned.
2 Changed the settings over to ASCII and still nothing
3 added a ground terminal tied the COMM and a grounding bar on the analyzer to it still nothing
4 changed the commands to AWA still nothing
5 switched wires still nothing

 

[Ken Roach]

I suppose I'd have to see your program logic or test it myself.

I generally test by setting the port to RS-232, connecting it with a null-modem cable to a computer running RealTerm (or PuTTy, or Hyperterminal) and testing it that way. Then at least I'm certain what's coming out of the port.

You said that the ASCII instructions 'send all the characters' with no problem. So the problem is on the slave device side, isn't it ?

Since PuTTY works, and the MicroLogix doesn't, the task is to find out the difference.

 

[gumba00]

I dont think it is the slave device.
I tested the communications coming out with PuTTy and got the commands.
I tested the same communications going in into the slave device with PuTTy and can program just fine.
I am going to check the terminating resistance today just to double check. Past that im out of ideas.