Advertisements
Advertisements
Question
Consider Accumulator contains FFH and register C contains 4DH. Execute following instructions one after the other and write contents of Accumulator after each instruction:
- XRA A
- ADD C
- CPI 4D H
- SUB C
Solution
- XRA A = 00H
- ADD C = 4DH
- CPI 4D H = 4DH
- SUB C = 00H
Accumulator (A) = FFH = 1111 1111
Consider weight,
Register C ∴ 4D = 0100 1101
(i) XRA A
Accumulator = A = FFH 1111 1111
XRA = A = FFH 1111 1111
0000 0000
0 0
∴ After XRA A accumulator content = 00H
(ii) ADD C
Accumulator (A) = 00H 0000 0000
ADD C = 4DH 0100 1101
0100 1101
4 D
∴ After ADD C accumulator content = 4DH
(iii) CPI 4D H
Accumulator A = 4D 0100 1101
CPI = 4D 0100 1101
1011 0010
+ 1
1011 0011
+ 0100 1101
Complementary
carry 1 0000 0000
0 0 0
Cy = 0 and Z = 1
∴ After CPI 4D accumulator content = 4DH
Because of immediate comparison, the accumulator's content does not change.
(iv) SUB C
ACcumulator A = 4D 0100 1101
SUB C = 4D 0100 1101
1011 0010
+ 1
1011 0011
Complementary carry 1 0100 1101
0 0000 0000
0 0
∴ After SUB C accumulator content = 00H
