ControlLogix Serial Port Echo On/Off Control

[skyfox]

Is it possible to control the Echo Mode of the built in Serial Port via ladder Logic?

For example, Turn off Echo During Transmitting only so when the receving device sends a Echo for a Command Transmit that was Originated from Controllogix and in turn, Controllogix does not Re-Echo the Echo of the original transmit received from the device?

Thanks

 

[Ken Roach]

It's not easy. Echo is an element of the Serial Port Configuration, which isn't easily changeable during runtime. You have to send a Configuration message, then execute an "Apply Configuration" command.

You certainly wouldn't be able to do this in between packets.

I happen to be writing a custom protocol driver with the 1734-485ASC module this afternoon, so echoes and strings are on my mind.

 

[JeffKiper]

Ken it's Sunday you should be relaxing having an nice day yelling at the TV over some football acton

 

[skyfox]

Thanks for the info Ken,

I have to watch for an echo for the commands that I send to the device, and send an echo for each byte of response (data) that I get from the device. Is it OK to use more than one "AWT" & "ARD" instructions where each "ARD" is looking for a byte of data and Each "AWT" writing or echoing a byte of data? ( I.e. Moving a byte of data from the buffer each time a byte is received, and if it is an echo that I need to send then re-tranmit it to the device after verifying the data was valid)

I tried this approach (without Using the ECHO Mode) with a single ARD/AWT pair and uing an array to store the Sent/Received data. It did not play well. So thinking about using multiple Instructions. Wondering if it is ok to have these ARD/AWT's on the same subroutine or better to seperate them out? I used logic to lock out reads and writes so they were not happening or being called on at the same time.

Thanks again.

 

[Ken Roach]

When the Seahawks hired Pete Carroll, I had to stop watching football on Sundays. The sight of him on a sideline still makes steam shoot from my ears.

Skyfox, writing serial port protocols with the ControlLogix ASCII instruction set isn't pretty. You need to be absolutely sure that each ASCII instruction is complete before you attempt to execute another (and that includes the Clear Buffer instructions), or the channel will enter a state that looks a lot like being "locked up". Not fun.

It's definitely possible to do manual echoing, and it sounds like your application needs it.

I'll mention that the absolute best value in serial protocol intercept and analysis is the EZ-Tap from Stratus Engineering. The number of hours it's saved me and the aggravation of cables and adapters and wondering if I got the wiring right is many multiples of its purchase price.

If you do ASCII, or Modbus, or any other serial protocols. the EZ-Tap should be in your toolkit.

 

[JeffKiper]

I have to second Ken's suggestion on the EZ Tap I bought one a few years ago. It goes on every job I go on.
I used it to figure out that my virtual DOS PC want passing the serial data to a PLC that no one had connected to in years and it wasn't running. So when I tried to connect was it the PLC, cable, settings, PC?
I use don't use the software that comes with the the EZ Tap. It does have a few nice features like a split screen from port to port. I use Docklight for 98% of all the serial monitoring needs.

 

[Mickey]

When the Seahawks hired Pete Carroll, I had to stop watching football on Sundays. The sight of him on a sideline still makes steam shoot from my ears.

USC's coeds would welcome him back. He had a really nice beach house.