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

USB bus will answer all your requirements. It might be very simple usb device with only control pipe to send request to your device or you can add an interrupt pipe that will allow you to notify host about changes in your device. There is a number of simple usb controllers that can be used, for example Cypress or Microchip.

Protocol on top of the transfer is really about your requirements. From your description it seems that simple synchronous protocol is definitely enough. What make you wander and look for additional approach? Share your doubts and we will try to help :).