Hmmmmmm...... probrably has to do with the stack pointer. Do I have to declare the stack pointer? I thought the 8051 will automatically allocate the space inside its internal memory. I didn't declare it beforehand. Maybe it clashes with some of the data I have stored in the internal memory throughout the running of the program. How many bytes of memory do I need for the stack (for CALL function) anyway?

But anyhow, isn't it funny that by simply changing the positions of my functions, the program will work, and is stable (I've tested it many times). And by changing to other positions, it will become messed up all over again?

To Erik, my mistake. I have accidentally written 'assembler' for 'compiler'. Sorry.

To Alan, I just put the whole block of functions in one document.

Thanks ppl! Hope you can provide some insights on the above matter.