The assembly instructions of Main program and Subroutine MYADD are given below.

Question

The assembly instructions of Main program and Subroutine MYADD are given below.

Assume that the starting address of main program is $2000 and Subroutine MYADD is 2FE0.

Sum dc.B 0

Main

LDS #$1FFF LDAA #51

LDAB # 49 JSR MYADD

Loop

BRA LOOP

MYADD

PSHA

PSHB

ABA

STAA Sum PULB PULA

RTS

In front of each instruction specify the addressing mode

Show the contents of stack after JSR MYADD instruction is executed

Show the contents of stack after PSHB instruction is executed

Show the contents of stack after RTS instruction is executed

Explanation / Answer

Main
LDR R1 , N ;
MOV R0 , #0 ;
BL SUMUP ;
LDR R3, =SUMP ;
STR R0, [ R3 ] ;
B STOP
SUMUP PROC ;
ADD R0 , R0 , R1 ;
SUBS R1 , R1 , #1 ;
BGT SUMUP ;
BX LR ;
ENDP
N DCD 5
ALIGN
STOP
END

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