So assuming you get a driver loaded, it will probably look like a serial port. The big issue with 485 software, is that you may be operating in a mode where the transmit and receive pairs are tied together onto a single pair so that you see whatever you transmit. In this case, you need to turn off the transmitter after sending a message out to your instrumentation in order to get a reply back. In transmit mode the controlling transmitter is driving the line levels and only one transmitter can do that at a time. The trick here is determining when you've finished sending. Even with a 1 character hardware send buffer you may get a buffer free interrupt before the last bit is out. If you turn the line around too soon, you'll clobber the last few bits (or bytes) of the message you just sent. Two solutions without an interrupt that tells you that the transmit buffer is truly empty)
- 1 - wait a bit until the buffer is surly free
2 - look at the data you've just sent until you see it all (since the receive pair is tied to transmit)
This latter method will work with a standard 232 serial port driver.
I typically used an external 232 - 485 converter which has hardware built in to turn the line around as needed.