Reference no: EM131531111

Question: Write a subroutine called, ADDABC, that performs the operation c : A + B. The three variables A, B, and C are all word (i.e., 16-bit) values. Test your program on the 68000 simulator. Your calling code and subroutine should have the following features:

• The parameters A and B should be passed on the stack to the procedure by reference (i.e., by address).

• Since parameters A and B are adjacent in memory, you need to pass only the address of parameter A to the subroutine (because the address of parameter B is 2 bytes on from parameter A).

• Parameter C should be passed back to the calling program on the stack by value.

• Before you call the subroutine, make room on the stack for the returned parameter (i.e., parameter C).

• After calling the subroutine, read the parameter off the stack into data register DO (i.e., DO should end up containing the value of A + B).

• The subroutine ADDABC must not corrupt any registers. Save all working registers on the stack on entry to the subroutine, and restore them before returning from the subroutine.

• When you write your code, preset the stack pointer to a value such as $1500 (by using either MOVEA L 11$ 15 00 , A7 or LEA $1500,10). Doing this will make it easier to follow the movement of the stack while your program is running.

• Make certain that you are operating with the correct operand sizes. Use .w for data values and for addresses and pointers.