1769-ASCII module receives delimiter only

This is maddening. I'm developing a new application where a 1769-L32E with a 1769-ASCII module is communicating with a Tegam micro-ohmmeter.

Everything works great with a PC terminal connected to the ASCII module. When I connect the two together for real, the ASCII module sends the commands to the Tegam correctly but when the Tegam responds the ASCII module only shows receiving a CR character. The RxID updates showing that it did receive.

I've verified my cable. I've built an RS232 sniffer and connected the terminal - the correct message appears there. I've pumped the message through my interface cable with the terminal and the ASCII module receives it correctly. I've examined the messages with the terminal in hex mode and there are no funny extra characters. I've checked my Baud Rate on the module. I've set it to Include Delimiter $R. I've followed all the instructions in the Rockwell manual - this is how I got it working with the terminal.

For some unknown reason the ASCII module won't recognize what the Tegam sends out its TX pin.

Suggestions? Time to get the scope out?

Thanks
Joe T.

Following up for interested parties - I finally got it figured out.

I had the wrong number of stop bits configured in the ASCII module. The documentation in the Tegam manual said 8N2 and I took this as gospel so I never checked it.

I use Bray's Terminal (terminal.exe) for all my serial troubleshooting. It is a great little program and has never failed me. Until now. I had it set to 8N2 and all communications to the Tegam worked perfectly using Bray's terminal.

We did get the scope out and our particular scope (Rigol DS1054) has a mode where it can decode RS232 characters. I received junk characters on the scope compared to what the terminal was receiving, but the character count was the same.

So we mapped out the characters on the scope and from the terminal in binary format and realized the characters on the scope matched the terminal characters but all the bits on the scope were shifted left by one. This was a data frame size problem. Going back into the ASCII module configuration and changing it to 8N1 made the problem go away.

The weird thing was Bray's terminal worked perfectly, whether there was one stop bit or two in its configuration panel. I'm guessing there's code under the hood to dynamically adapt to what's coming in, but in this case it sent me on a wild goose chase.

I don't know what conclusion to draw here, other than I was fighting two problems at the same time.

A scope! A scope! My kingdom for a scope!