I hope I got it as well, but I'll give it a try:
When dividing a number with DIV then it returns the result in AX and the modulo in DX.
Communicating with a microchip can easily be done via the RS-232 (COM) Port. Have a look in you OS-environment to find the port you want to use. Alternatively you can have a look in the net as mostly the ports have the same address. There is a way, and not even hard, to find the 232-port in assembly but I can find the website in the moment and don't have my source-code on this computer. Sorry.