Protocols used to talk between an embedded CPU and a PC

Question

I am building a small device with its own CPU (AVR Mega8) that is supposed to connect to a PC. Assuming that the physical connection and passing of bytes has been accomplished,

Answer 1

Adam Liss makes a lot of great points. Simplicity and robustness should be the focus. Human readable ASCII transfers help a LOT while debugging. Great suggestions.

They may be overkill for your needs, but HDLC and/or PPP add in the concept of a data link layer, and all the benefits (and costs) that come with a data link layer. Link management, framing, checksums, sequence numbers, re-transmissions, etc... all help ensure robust communications, but add complexity, processing and code size, and may not be necessary for your particular application.