i am actually writing a program to program an 8051 chip to control an external device that has toggle switches and LEDs on it and there should be 16 digital inputs from the toggle switches(there are only 8 toggle switches) and 8 digital outputs to be shown on the LEDs.
Below is a diagram on what i should do:

program(from computer)--USB cable-->board with 8051 chip

--serial cable-->external device( with 8 toggle switches and LEDs

hope you all can understand the diagram.

thanks