Examining the CY flag and the stack

OBJECTIVES:

- To examine the flag bits of the PSW.
- To examine the stack.

ACTIVITY 1
Write and assemble a program to add the following data and then use the simulator to examine the CY flag.

92H, 23H, 66H, 87H, F5H

ACTIVITY 2
Write and assemble a program to load values into each of registers R0 - R4 and then push each of these registers onto the stack. Single-step the program, and examine the stack and the SP register after the execution of each instruction.

ACTIVITY 3

Write and assemble a program to:
(a) Set SP = 0D,
(b) Put a different value in each of RAM locations 0D, 0C, 0B, 0A, 09, and 08,
(c) POP each stack location into registers R0 - R4.

Use the simulator to single-step and examine the registers, the stack, and the stack pointer.

1. Find the value of the CY flag after the execution of the following code.

            (a)        MOV   A,#85H 

                        ADD   A,#92H

            (b)        MOV   A,#15H 

                        ADD   A,#72H

            (c)        MOV   A,#0F5H

                        ADD   A,#52H 

            (d)       MOV A,#0FF

                       INC A

2. Upon reset, what is the value in the SP register?

3. Upon pushing data onto the stack, the SP register is _____________ (decremented, incremented).

4. Upon popping data from the stack, the SP register is ___________ (decremented, incremented).

5. Can you change the value of the SP register? If yes, explain why you would want. A SP is a small register that stores the addresses of the program request in a stack, which stores data from the top down. The most recently request always takes from the top.

6. The stack uses the same area of RAM as bank __4____.