Anil,

If you are using a 12MHz clock on a standard 8051 each instruction takes about 12 oscilator cycles, so doing something like

start:

cpl p0.1
jmp start

will take 24 cycles, so that's 0.5Mhz.

You'll need at least a 24MHz clock to generate a 1MHz pulse on a standard 8052....

Chris.