Ab 1785 Ke

I am working with an AB PLC that has a 1785 KE Data Highway Plus to RS232 Card installed to communicate with a PC Based system. I can not find any MSG or BT instructions that pertain to the PC based system. I do not have access to the PC System so I don't know what programs are running in it. Are there any other instructions in the PLC that I should look for, or can the PC progrom transfer data without any PLC logic instructions?

You didn't mention which PLC you are using. I am guessing that it is an older model PLC-5 such as a 5/15 or 5/25 seeing that those units do not have the built in serial port.

My guess is that the polling or "messaging" is probably taking place from the PC system to the PLC rather than the other way around.

If you are working with a newer model PLC-5 then look for an AWT ASCII Write instruction. Actually I don't think will work now that I think about it.

A MSG is the only instruction I can think of that could send something over DH+ and through the RS232 bridge.

OG

Thanks OG . It is a PLC5. Would the PC based system have to use third party software to poll that data or could it be written in their code? In either case could they read and write data without any plc code? If seperate software must be used, what are some examples of such software?
Thanks,
Keith

Most PC application builders buy a DF1 protocol driver and let it handle the low-level communications, and use C calls or a higher-level interface like OPC or DDE to connect to the driver.

RSLinx is Rockwell Software's driver, but DF1 protocol is simple enough that many low-cost single-purpose drivers are sold by companies like Software Toolbox or Kepware.

Some PC applications code their own. There was a thread earlier this week where a guy was just using Print statements from VB5 to send simple DF1 commands to a MicroLogix.

What are you being asked to do with this system ?

We are losing communications between the two systems. The maker of the PC system blamed it on the PLC before I began working here two months ago. I am trying to eleminate any PLC issues before contacting the PC system manufacturer. Also, I am comfortable with PLC programming and systems, but have had little experience with the PC based systems. I thought it would be a good time to start learning them based on their popularity.