ASCII Commands on a Ctrlogix 1769-L23E QB

[CBowman]

Hey Everyone,

I'm trying to communicate to an external device using ASCII Read and Write commands with RSLogix 5000. I need to Write an ASCII command to get the device to start spitting out an ASCII output, then I need to Read that output.

The termination of my ASCII string is <cr><lf> but I'm not certain how or where to configure this in RSLogix.

I've attached the sample program for review if anyone can give me some ideas.

 

[Ken Roach]

Do you need to send "S3UH<CR><LF>", for a total of six bytes ?

How fast do the replies come, and what length are they ? Are they also terminated with <CR> <LF> ?

 

[daba]

I'm not at a RSLogix machine right now, but I do know the STRING tag editor in RSLogix5000 allows you to put control characters in.

Failing that, if you are using a SINT array for your ASCII data, put these as your terminators....

16#0D = <cr>
16#0A = <lf>

 

[Ken Roach]

I spent a little time refreshing my recollection of the ASCII instruction set. It's very important to remember that only one ASCII instruction can execute at a time, so it's easy to accidentally jam the buffer full.

Set the serial port User mode settings back to defaults; you want both the Append and Termination bytes to be #1= $r and #2 $l. Those are Carriage Return and Line Feed.

Here's a short example, written for a 1756-L55 with v16 firmware. I don't have a v17 controller handy.

 

[CBowman]

Thanks Ken!

I will head back to the PLC now and see what happens. I think I have the termination and append settings wrong, so hopefully that will help!

Daba, thanks for your input as well. I will take this and see what I can do.