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Binary Coded Decimal (BCD)
The binary-coded decimal is "a numerical system using a binary number to
represent a decimal number".
A decimal number 157, for example, is expressed as shown below.
1
2
5
10
Digit number
7
(100) (10) (1)
0001 0101 0111
Power of digit
Decimal
Binary bit weights
BCD
842
1
8 2
14
8
14 2
In BCD, decimal numbers 0 to 9999 (the biggest 4-digit number) can be
represented by 16 bits.
The diagram below shows the bit weights of BCD.
8000
4000
2000
1000
800
400
200
100
80
40
20
10
8
4
2
0 000 0001 0101 0111
1
Thousand digits
Hundred digits
Ten digits
Unit digit
BCD is used for the following signals.
1) Output signals of digital switches
2) Signals of seven-element display (digital display)
0 1 2 3 4 5 6 7 8 9
1(0)
2(0)
4(0)
8(0)
COM
(1)
(0)
(0)
(0)
(0)
(1)
(0)
(0)
(1)
(1)
(0)
(0)
(0)
(0)
(1)
(0)
(1)
(0)
(1)
(0)
(0)
(1)
(1)
(0)
(1)
(1)
(0)
(1)
(0)
(0)
(0)
(1)
(1)
(0)
(0)
(1)
BCD code digital switch