Question

Explain the function of following instructions of Intel 8085 :

PUSH B

Answer 1

PUSH B [PUSH REGISTER PAIR ON STACK]

Formal: [[SP] - 1] ← [rh]

            [[SP] - 2] ← [rl]

            [[SP] ← [SP] - 2

Addressing: Register indirect addressing

Bytes: 1 byte

Flags: None

Comment :

1) The contents of the higher order register of register pair rp are moved to the memory location, whose address is one less than the content of stack points.

2) The contents of the low order register or register pair rp are moved to the memory location whose address is two less than the content of stack pointer.

3) The stack pointer is determined by two. rp may be any one of the B (B & C), D (D & E), H (H & L)

Example:

Let [SP] = D015 H, [B] = 25 H and [C] = 55 H

Instruction: PUSH B

After execution: [D014] = 25 H

                        [D013] = 55 H

                  and [SP] = D013 H