Question

How are subroutines called? Explain with an example.

Answer 1

A subroutine is called using a CALL instruction. CALL saves the return address and jumps to the subroutine; when the subroutine finishes, a RET instruction pops the return address back into the program counter, so execution returns to the caller.

Example:

4004: MOV A, C
4005: ADD B
4006: CALL UPDDT
4009: HLT

UPDDT: (subroutine instructions)
       RET