Logix and Serial Issues

I am having some troubles with a device on a machine. The device communicates serially to my PLC. I am sending data without a problem, but for some reason the device will not send me back data for me to compare in the PLC that data was sent properly and its okay to run a part. The only information the device is giving back to me is the ASCII "ACK" character telling me that the device received a valid block of data. I have checked out all hardware concerns and they check out. Also all settings on the device are correct. I know I'm missing one key piece and for the life of me I cannot figure out what it is. Can anyone help here to give me some words of wisdom?

What is the target device? I would guess it isn't setup to give a response other than a "ACK". Have you started snooping on the serial lines yet. I have on accident used an "AWA" (I think) that sends out an append character. I didn't need that in my string so the target device responded that it got an invalid command.

There are many thousands of serial devices you might connect to a PLC, and many hundreds of serial protocols, so you're going to have to help narrow it down by posting some basic information about the device and its configuration.

Thanks for the replies but found the issue not long after my post. I thought i was sending it an "ENQ" command to receive the data stored in the device however i failed to double check that the ENQ command was actually being sent and it wasn't. Once i smoothed out that everything was up and running.