Some of your posts give the impression that the switches and LEDs are directly connected to the 8051, some show a serial link between the LEDs/switches and the 8051. You also seem to want to connect the 8051 to the PC using USB rather than RS232 in order to download code to it. This seems strange.

I think you are very confused - please describe in detail what you are trying to achieve. Ideally, draw a block diagram and explain what each block is supposed to do and why you think it should be done that way. Don't forget to explain what the purpose of the whole system is.

Lots of people are wasting time replying to your various posts after trying to guess what you are trying to do. You will get much more useful answers if you explain more clearly.