BCD Addition
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BINARY-CODED DECIMAL
BCD Addition - Continued
Neets Module 13-Introduction to Number Systems and Logic Circuits
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1-60
The BCD equivalent of 264
_{10}
is 001001100100
_{BCD}
. To convert from BCD to decimal, simply reverse
the process as shown:
BCD Addition
The procedures followed in adding BCD are the same as those used in binary. There is, however, the
possibility that addition of BCD values will result in invalid totals. The following example shows this:
Add 9 and 6 in BCD:
The sum 1111
_{2}
is the binary equivalent of 15
_{10}
; however, 1111 is not a valid BCD number. You
cannot exceed 1001 in BCD, so a correction factor must be made. To do this, you add 6
_{10}
(0110
_{BCD}
) to the
sum of the two numbers. The "add 6" correction factor is added to any BCD group larger than 1001
_{2}
.
Remember, there is no 1010
_{2}
, 1011
_{2}
, 1100
_{2}
, 1101
_{2}
, 1110
_{2}
, or 1111
_{2}
in BCD:
The sum plus the add 6 correction factor can then be converted back to decimal to check the answer.
Put any carries that were developed in the add 6 process into a new 4-bit word:
Now observe the addition of 60
_{10}
and 55
_{10}
in BCD:
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