ExamplE 2.58 Perform subtraction of BCD numbers using 9’s complement.
(a) (64 − 25)
BCD
(b) (504.4 − 686.5)
BCD
Solution
(a) Take 9’s complement of (N)
BCD
= 25 and add it to (M)
BCD
= 64
Nine’s complement of 25 = 74
BCD code of 9’s complement of 25 = 0111 0100
000
(M) =
64
⇔
01100100
Nine’s complement of (N) =
7401110100
(M) + (9’s complement of (N)) =
138011011000
11011000
Convert binary into BCD01100000
100111000
End carry (digit in third digit after addition) is one, so add 1 to the LSD place
positive sign
(M) + (9’s complement of (N)) =
3800111000
Add 1 to LSD =+
1
+
1
(M)−(N) =+
39Ans.
⇔
00111001Ans.
39
(b) ...
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