Programming

User an appropriate layering in your software so that only the bottom bit is concerned about RS232, the higher levels should work on any stream at all, so if, for example you weren't directly connected to the device and it was a remote machine that did, you could have an SSH/SSL/TCP connection between the two machines and your code happily talk over that.

no matter what language you use, it's important to try to keep generic things generic. I like the C++ templates approach. It gets a bit complicated, but it's well worth it because it provides an incredibly versatile and portable way to deal with the io. There are some real good books that explain how to take advantage of the iostreams library. It takes a little effort to find the right balance between 'overly complicated' and usefulness.