Question 9626 – Machine-Instructions

Consider the following assembly language program for a hypothetical processor. A, B, and C are 8 bit registers. The meanings of various instructions are shown as comments.

     MOV B, # 0   	;   B ← 0
     MOV C, # 8	        ;   C ← 8
Z :  CMP C, # 0	        ;   compare C with 0
     JZX	        ;   jump to X if zero flag is set
     SUB C, # 1	        ;   C ← C - 1
     RRC A, # 1 	;   right rotate A through carry by one bit. Thus:
                        ;   if the initial values of A and the carry flag are a7...a0 and
                        ;   c0 respectively, their values after the execution of this
                        ;   instruction will be c0a7...a1 and a0 respectively.
     JC Y	        ;   jump to Y if carry flag is set
     JMP Z	        ;   jump to Z
Y :  ADD B, # 1	        ;   B ← B + 1
     JMP Z	        ;   jump to Z
X :	

If the initial value of register A is A₀ the value of register B after the program execution will be

Correct Answer: B