Question

4. Consider the following assembly-language program. Starting values: [A] = $60, [B] = $80, [$C300] = $20, [$C301] = $40 (Hint: [$C300) means "contents of memory location $C300".) $C300 $C301 ADDA LDAB SBA BEO STAA STAB WAI X1 $1301 $C300 X1: ; "WAI" basically means "stop" What values are in A, B, memory location $C300, and memory location $C301 when the program finishes? [A] = — [B]= _ [$C300] = - [$C301) =

this is assembly language for HCS12 / 9S12

Answer 1

Solution:

Given, [A] = $60; [B] = $80; [$C300] = $20; [$C301] = $40.

ADDA $C300 ; A $\leftarrow$ [A]+[$C300] i.e. $60 + $20 = $80 will store in A. Now the value [A] = $80.

LDAB $C301; B = [$C301] i.e. $40 will load in [B]. Now the value of [B] = $40.

SBA    ; A  $\leftarrow$ [A] - [B] i.e. $80 - $40 = $40 will store in [A]. Now [A] = $40.

BEQ X1 ; In the above subtraction instruction [A] > [B]. So, it will not jump to X1 loop and proceed to next line.

STAA $C301 ; [$C301] $\leftarrow$ [A] i.e. $40 will store in memory location [$C301].

X1 : STAB $C300 ; [$C300] $\leftarrow$ [B] i.e. $40 will store in memory location [$C300].

WAI.

After execution of the above program, [A] = $40; [B] = $40; [$C300] = $40; [$C301] = $40.

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