LOGIX 5000 TCP socket ASCII messaging

[statikjak]

I have a bit of an odd situation. I'm having trouble sending ASCII commands over an open TCP socket. The problem is that I have a device that my only option for giving it commands is by sending ASCII commands over serial. I have a serial device server to convert the serial to ethernet so I can try to communicate with it. Here's a link to what I'm using: https://shop.usriot.com/modbus-serial-to-ethernet-converters-usr-tcp232-410s.html

I am working with a 1756-L72 and 1756-EN3TR as my ethernet connection. I am using the TCP Client Socket AOI that has been put out by Rockwell.

So, overall, through the web interface for the converter, I can send ASCII commands to my device. Also, I can create an open socket in the PLC to the converter. I can verify this in both the PLC (the AOI is running) and in the converter (indicates an open socket).

However, I try to use the write command through the PLC AOI, and nothing happens. The message executes and indicates finishing without error, but nothing happens. No message is received by the device, and there is no indication in the converter.

When I get into the diagnostics for the 1756-EN3TR, I can see that there is an open socket and that socket writes are occurring.

I'm not sure what I'm missing here. I don't know why the ASCII commands won't pass through. Any thoughts on where I'm getting hung up?

Thanks all!

 

[drbitboy]

Does the device have a Modbus ASCII interface, or just a generic ASCII interface?

 

[statikjak]

I believe I'm looking at a generic ASCII interface. None of the MODBUS options are on/set and I can give it commands through my serial-to-ethernet converter. It's would seem like the data I'm sending in the PLC is not being received by the converter.

I also have no indication of it being modbus in the device's manuals. It only lists "ASCII encoded command protocol"

 

[drbitboy]

I would first try using Hyperterminal or similar on a PC with a serial to see if you can receive data from the converter. Once you have that working, then try to talk to the device using Hyperterminal from the PC.

That way you can ensure you have the cabling, pinouts, and communications parameters, all correct on both sides.

 

[Contr_Conn]

Based on the link that you have posted, it does look like Modbus converter and even title said that.
Or may be it's configured for the Modbus converter instead of just plain ASCII?

 

[statikjak]

Hmmm, I have a feeling that it might be Modbus. I tried connecting to it through PuTTY as well, and again, I could establish a socket, but no commands seemed to continue through that I type into the terminal.

If it is indeed Modbus, I'm just hosed then, correct? I don't think I have any other options in the PLC logic?

I'm trying to go down the route of a data protocol converter from Red Lion, but that has it's own learning curve.

 

[drbitboy]

Wait a minute, a Logix 5000/ControlLogix system does not have Modbus TCP built-in? Or at least available via an AOI?

Or is the problem that the *device* is Modbus ASCII, and the converter can convert, in Modbus mode, from Modbus TCP to Modbus RTU (serial binary), but not to Modbus ASCII?

Obviously you could roll you own socket app to build Modbus ASCII commands and send them to the converter operating in non-Modbus, ASCII-conversion-only mode, but I agree for the time required to do that there are probably better approaches out there.

 

[drbitboy]

Can you run the serial line from the converter back to the PC and another PuTTY instance, and see what shows up?

 

[Saffa]

Wait a minute, a Logix 5000/ControlLogix system does not have Modbus TCP built-in? Or at least available via an AOI?

Or is the problem that the *device* is Modbus ASCII, and the converter can convert, in Modbus mode, from Modbus TCP to Modbus RTU (serial binary), but not to Modbus ASCII?

Obviously you could roll you own socket app to build Modbus ASCII commands and send them to the converter operating in non-Modbus, ASCII-conversion-only mode, but I agree for the time required to do that there are probably better approaches out there.

The OPs serial device isn't expecting modbus. The issue is that he has a serial to TCP converter designed for modbus, instead of a plain serial to ethernet converter.

Modbus TCP isn't just ethernet encapsulated serial data, so those converters have to do more than just strip off the TCP header and put it back out on the serial port.

MOXA have several plain ol serial to ethernet converters that should do the trick.

 

[drbitboy]

The OPs serial device isn't expecting modbus. The issue is that he has a serial to TCP converter designed for modbus, instead of a plain serial to ethernet converter.

Modbus TCP isn't just ethernet encapsulated serial data, so those converters have to do more than just strip off the TCP header and put it back out on the serial port.

MOXA have several plain ol serial to ethernet converters that should do the trick.

The converter quoted by OP can do plain serial or Modbus. It is not clear from OP (see their latest post) whether the serial device is Modbus or not.