Dear Hu,

A very valiant first effort, especially to use interrupts in your first effort, but I think you need to review the tutorials on the 8052 timers. You seem to be doing some awfully complicated things in your timer interrrupt.

Have you read the "8052 Bible" in the links section here ?

If you use timer2 instead, it can automatically reload itself, so you don't need too. Every time the interrupt is called, you just invert out the output bit.

If your variant has the Compare/Capture unit, then you can do your 50 hz signal with no processor intervention.

Steve