Without knowing anything about '51 ASSY I can tell that the above program is far too complex for such a small task as driving a stepper motor.

The problem is really simple. All You need is a counter and then a routine that converts this counter into motor pin drives.

The stepper needs the 2 or 3 lowest bits of this counter depending if You are going to use half steps or not.

The subroutine that does the conversion is just an if-then-else or case( n) .... construct with 4 or 8 branches. You just simply compare the lowest bits with constants and then branch to corresponding output pin setup. Make a truth table so this is easy to code.


Now, increment the counter then call the converion and the motor will step once to some direction. Decrement the counter and call the converter and motor steps the other direction.

Add timer and the switch handling and there You are.