practical 8 call and subroutine

7/27/2019 Practical 8 Call and Subroutine

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8.1

AIM: - TO STUDY ABOUT STACK & SUBROUTINE

PUSH RP :

Store register pair (BC,DE,HL & PSW) on stack

This is a 1-byte instruction

It copies the contents of the specified register pair on the stack as described below.

The stack pointer register is decremented, & the contents of high order register(e.g,

register B) are copied in the location shown by the stack pointer register.

The stack pointer register is again decremented, & the contents of the low- order

register (e.g, register C) are copied in that location.

POP RP :

Retrieve register pair (BC,DE,HL & PSW) from stack

This is a 1-byte instruction

It copies the contents of the top two memory locations of the stack into the specified

register pair.

First, the contents of the memory location indicated by the stack pointer register are

copied into the low-order register (e.g,register L), then the stack pointer register is

incremented by 1.

The contents of the next memory location are copied into the high order register

e.g,register H), & the stack pointer register is again incremented by 1.

INSTRUCTION

OPCODE

OPERAND

NO. OF

BYTES

DESCRIPTION

CALL 16-bit 3 The program sequence is transferred to the address

specified by the operand. Before the transfer, the

address of the next instructions to CALL ( the contents

of the program counter) is pushed on the stack

CC 16-bit 3 Subroutine is called if Carry = 1.

CNC 16-bit 3 Subroutine is called if Carry = 0.

CP 16-bit 3 Subroutine is called if Sign = 0.CM 16-bit 3 Subroutine is called if Sign = 1.

CPE 16-bit 3 Subroutine is called if Parity = 1.

CPO 16-bit 3 Subroutine is called if Parity = 0.

CZ 16-bit 3 Subroutine is called if Zero = 1.

CNZ 16-bit 3 Subroutine is called if Zero = 0.

RET 1 The program sequence is transferred from the subroutine

to the calling program. The two bytes from the top of

the stack are copied into the program counter & the

program execution begins at the new address. The

instruction is equivalent to POP program counter.

RC 1 Return to main program if Carry =1.

ATMIYA INSTITUTE OF TECHNOLOGY & SCIENCE, RAJKOT

Subject:

Microprocessor and

Interfacing

Title:

To study Instructions for Stack and Subroutine

Experiment No.08DATE:

Rev. No.

1.00


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8.2

RNC 1 Return to main program if Carry =0.

RP 1 Return to main program if Sign = 0.

RM 1 Return to main program if Sign = 1.

RPE 1 Return to main program if Parity = 1.

RPO 1 Return to main program if Parity = 0.

RZ 1 Return to main program if Zero =1.

EXERCISE

1) Read the following program & answer the following questions given below.

Line no. Mnemonics

1LXI SP,0400H

1 LXI SP,0400H

2 LXI B,2055H

3 LXI H,22FFH

4 LXI D,2090H5 PUSH H

6 PUSH B

7 MOV A,L

| |

| |

20 POP H

a) What is stored in the stack pointer register after the execution of line 1?

b) What is the memory location of the stack where the first data byte will be stored?

c) What is stored in memory location 03FEH when line 5(PUSH H) is executed ?

d) After the execution of line 6 (PUSH B), what is the address in the stack pointer register,

& what is stored in stack memory location 03FDH ?

e) Specify the contents of register pair HL after execution of line 20 (POP H).

2) Read the following program & answer the questions.

2000 LXI SP,2100H DELAY: 2064 PUSH H

2003 LXI B,0000H 2065 PUSH B

2006 PUSH B 2066 LXI B,80FFH

2007 POP PSW LOOP :2069 DCX B2008 LXI H,200BH 206A MOV A,B

200B CALL 2064H 206B ORA C

200E OUT 01H 206C JNZ LOOP

2010 HLT 206F POP B

2070 RET

a) What is the status of the flags & the contents of the accumulator after the execution of

the POP instruction located at 2007H ?

b) Specify the stack locations & their contents after the execution of the CALL

instruction(not the CALL subroutine).

c) What are the contents of the stack pointer register & the program counter after theexecution of the CALL instruction?



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8.3

d) Specify the memory location where the program returns after the subroutine.

e) What is the ultimate fate of this program ?

3) Write a program to clear all the flags & prove that DCX instruction does not affect Zero flag

but DCR instruction affects it.( Use PUSH-POP)

4) Between memory locations F0F0H & FOFFH, 8 set of 16-bit data are stored. In each set firstbyte represents the number & the second represents dividends (number by which we have to

divide first byte). Do division for each set & store result (16-bit) in same memory location.

(Quotient in first memory location & remainder in second).

5) Three numbers X1 ,X2 ,X3 are stored from FOFOH. Write an ALP to compute

3

i.Xii =1

Store the result at memory locations FOF3H(lower byte) & FOF4H (higher byte). Usesubroutine technique to find i.Xi .



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8.4

GRADE LAB-INCHARGE H.O.D.

ANSWERS

A-1. (a) What is stored in the stack pointer register after execution of Line 1?Ans:- 0400H

(b) What is the memory location of the stack where the first data byte will be stored?

Ans:- 03FFH

(c) What is stored in memory location 03FFH when line 5 (PUSH B) is executed?

Ans:- FFH

(d) After the execution of line 6 (PUSH B) what is the address in the stack pointer

register & what is stored in stack memory location 03FDH?

Ans:- 03FDH, 20H

(e) Specify the contents of register pair HL after execution of line 20 (POP H).

Ans:- 22FFH

A-2. (a) What are the status of the flags & the contents of the accumulator after the execution

of the POP instruction located ?

ANS: - All flags are cleared, A =00H

(b) Specify the stack locations & their contents after the execution of the CALL

instruction (not the CALL subroutine).

ANS: - 20FEH = 0EH , 20FFH = 20H

(C) What are the contents of the stack pointer register & program counter after the

execution of the CALL instruction.

ANS :- SP = 20FEH , PC = 2064H

(D) Specify the memory location where the program returns after the subroutine.

ANS :- 2003H

(E) What is the ultimate fate of this program?

ANS :- Endless loop

A-3. lxi SP, 2100h

lxi B , 0000h

push B

pop psw

hlt

A-4. mvi D, 10h

BACK1: lxi H, F0F0h

mvi C, 00h

mov B, Minx H



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8.5

mov A, M

BACK: sub B

Inc C

cmp E

jnz BACK

mov M, A

dcx Hmov M, C

inx H

inx H

dcr D

jnz BACK1

hlt

A-5. lxi H, F0F2

mov E, M

mov A, M

call MUL3dcx H

mov E, M

mov A, M

call MUL2

dcx H

mov A, M

inx H

add M

inx H

adc M

mov A, Mmvi A, 00h

rlc A

inx H

mov M, A

hlt

MUL3: add E

MUL2: add E

mov M, A

ret


practical 8 call and subroutine

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