1734-485ASC to Display communications problem

[sharkster411 0]

Hello All, I'm currently attempting to use a 1734-485ASC module for a project to control a Message Display. This module is controlled by an SLC505 via Devicenet, and I am able to pass data to the module correctly. I have an RS-232 to RS-422/485 adaptor connected to my Laptop and am using Tera Term for testing. I can send ASCII commands to my Laptop and read them in Tera Term correctly. I can also send ASCII commands to the display and trigger the messages on the display correctly using Tera Term; however, when I send commands from the 1734-485ASC module to the display, I get nothing. Anyone have any ideas why this may be? Or does anyone know of any known "bugs" with this ASCII module that may allow it to pass to Tera Term, but not the module (incorrect EDS file config, etc.)?

[TravisPedley 20]

do you have a carraige return in the string you're sending from the ASC module to the display?  What you're describing usually means when you type in the data in the terminal and hit enter it will send a carraige return and line feed.  when you see the data from the plc to the teraterm how does it look when you send consecutive strings?

datadatadatadatadata

or

data

data

data

data

data

if it is all strung together, try adding a CR and maybe LF to the end of the string you're sending.

 

[sharkster411 0]

When I send the data, I have a delimiter set so it sends "DATA" just as it should look...at least the data received in Tera Term looks correct. The message display as diagnostics LED on the front that changes color whenever the display receives a command. This LED changes color like it should with every command sent via Tera Term. When I command the 1734-485ASC module to send the same ASCII data, the LED on the display never changes color. The "receive" LED on the back flashes like it should, but the display never acknowledges the command.

[kaiser_will 63]

Can your development PC and the message display be connected to the PLC at the same time?  Since your development PC can successfully send and receive data to/from the message display, having all 3 connected is a good way for your development PC to monitor the data traffic.

Once you have your development PC displaying the data stream, you can adjust the string write command in the logic to build the correct syntax to get working results.  Unfortunately with ASCII serial communications, this trial-and-error has been the best method I have used.

[sharkster411 0]

That is how I have everything connected currently. I can send ASCII from my PC to the Message Display, and it triggers. I can send ASCII from the 1734-485ASC module to the PC, and the ASCII commands appear to be correct; however, the Message Display acts as if it doesn't even see the ASCII coming from the 1734-485ASC module. They're all connected together in a small "RS-485 Network" per say, sitting on a bench. 

[kaiser_will 63]

Similar to what TravisPedley noted, you may need a carriage return command; it is possible the first command the PLC sent does not have an end character.  This seems very familiar to me.

Let's back up...what Logix instruction are you using to send ASCII information to the message display?

Try modifying the ASCII write instruction to append a carriage return.  

Have you tried to just send one character of data to be displayed on the message display?