Example on passing parameters through stack, Computer Engineering

Assignment Help:

Q. Example on Passing Parameters through Stack?

PROGRAM: Version 3

DATA_SEG               SEGMENT

                        BCD DB 25h; Storage for BCD test value

BIN DB?  ; Storage for binary value

DATA_SEG               ENDS

STACK_SEG   SEGMENT      STACK

DW 100 DUP (0); Stack of 100 words

TOP_STACK   LABEL    WORD

STACK_SEG   ENDS

CODE_SEG SEGMENT

ASSUME CS: CODE_SEG, DS: DATA_SEG, SS: STACK_SEG

START:           MOV AX, DATA                  ; Initialise data segment

 

MOV DS, AX                                    ; using AX register

MOV AX, STACK-SEG.      ; initialise stack segment

MOV SS, AX                         ; using AX register

MOV SP, OFFSET TOP_STACK; initialise stack pointer

MOV AL, BCD                      ; Move BCD value into AL

PUSH AX                               ; and push it onto word stack

CALL BCD_BINARY          ; Do the conversion

POP AX                                  ; Get the binary value

MOV BIN, AL                       ; and save it

NOP                                        ; Continue with program

 

; PROCEDURE: BCD_BINARY Converts BCD numbers to binary.

; INPUT   : None - BCD value assumed to be on stack before call

; OUTPUT   : None - Binary value on top of stack after return 

; DESTROYS: Nothing

BCD_BINARY PROC NEAR

                                 PUSHF     ; Save flags

                                 PUSH AX; and registers: AX

                                 PUSH BX; BX

                                 PUSH CX; CX

                                 PUSH BP; BP. Why BP?

                                 MOV BP, SP; Make a copy of the

                                                ; stack pointer in BP

                                 MOV   AX, [BP+ 12]; Get BCD number from

                                                ; stack. But why it is on 

 

; BP+12 location? Please note 5 PUSH statements + 1 call which is intra-segment (so 

; just IP is stored) so total 6 words are pushed after AX has been pushed and since it is 

; a word stack so the BCD value is stored on 6 × 2 = 12 locations under stack. Hence 

; [BP + 12] (refer to the figure given on next page).

MOV BL, AL; Save copy of BCD in BL

AND BL, 0Fh; mask lower 4 bits

AND AL, F0H; Separate upper 4 bits

MOV CL, 04; Move upper BCD digit to low

ROR   AL, CL; position BCD digit for multiply location

MOV   BH, 0Ah   ; Load 10 in BH

MUL BH; Multiply upper BCD digit in AL by 10

   ; The result is in AL

ADD   AL, BL; Add lower BCD digit to result.

MOV [BP + 12], AX   ; Put binary result on stack

; Restore flags and registers

POP BP

POP CX

POP BX

            POP AX

                                 POPF  

                                 RET  

BCD_BINARY       ENDP

CODE_SEG            ENDS

END   START  

 

Discussion: 

The parameter is pushed on stack before the procedure call. Procedure call causes the current instruction pointer to be pushed on to stack. In the procedure flags AX, BX, CX and BP registers are also pushed in that order. Hence the stack looks to be:

721_Example on Passing Parameters through Stack.png

The instruction MOV BP, SP transfers contents of the SP to BP register. Now BP is used to access any location in stack by adding appropriate offset to it. For illustration MOV AX, [BP + 12] instruction transfers the word starting at the 12th byte from the top of stack to AX register. It doesn't change the contents of BP register or top of the stack. It copies pushed value of AL and AH at offset 008Eh into the AX register. This instruction isn't equivalent to POP instruction. 

Stacks are useful for writing procedures for multi-user system programs or recursive procedures. It's a decent practice to make a stack diagram as above when using procedure call through stacks. This helps in reducing errors in programming.


Related Discussions:- Example on passing parameters through stack

Discuss the general procedure of booting process, Question 1 What are t...

Question 1 What are the different schemes in power management? Explain 2 Explain the functions of parallel port in detail 3 (a) List and explain the functions of keyboard

Show data representation for computation, Binary codes exist for any fundam...

Binary codes exist for any fundamental representation. Binary codes can be created for any set of discrete elements for example colors, spectrum, musical notes, chessboard position

Scsi bus - computer architecture, SCSI Bus:   Defined by ANSI - X3....

SCSI Bus:   Defined by ANSI - X3.131   50, 68 or 80 pins   Max. transfer rate - 160 MB/s, 320 MB/s. SCSI Bus Signals   Small Computer System Interface

Write a menu driven program to perform addition, Q. Write a menu driven pr...

Q. Write a menu driven program to perform addition and subtraction in base 5. Check that entered numbers are in base 5 or not else error message should be displayed.

Routines which handle dynamic processes, Q. Routines which handle dynamic p...

Q. Routines which handle dynamic processes? number of routines which handle dynamic processes:  int pvm_joingroup( char *group ) Enrolls calling process in a na

Three different types of convergences, Three dissimilar types of convergenc...

Three dissimilar types of convergences are: 1.  The convergence of e-commerce and wireless technology  2.  The Convergence of E-Commerce and IP Business-Grade Messaging 3

Explain the storage class static, Explain the Storage Class Static Th...

Explain the Storage Class Static The Storage Class Static : Static declarations have two important and distinct uses. The more elementary use is to allow a local variable to

Explain message, Differentiate between message switching, packet switching ...

Differentiate between message switching, packet switching and circuit switching Message switching: Recourse computer sends data to switching office that stores the data in

Physics, #questionabut diffraction ..

#questionabut diffraction ..

What is indexed addressing, What is Indexed addressing The location of ...

What is Indexed addressing The location of data is calculated as sum of an address specified by one of previous methods, and value of an index register. This allows an array of

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd