Page 76 - Computer science 868 Class 12
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The truth table is given below:
Octal Number B 2 B 1 B 0
0 0 0 0
1 0 0 1
2 0 1 0
3 0 1 1
4 1 0 0
5 1 0 1
6 1 1 0
7 1 1 1
Here B , B and B represent the OR gates where the binary outputs are obtained. If the Octal numbers are represented
2
0
1
by switches I0 to I7 then from the truth table we can conclude that
B = I + I + I + I 7
1
3
0
5
B = I + I + I + I 7
6
3
2
1
B = I + I + I + I 7
2
6
4
5
The logic circuit diagram of an Octal to Binary Encoder is as follows:
0
1
2
3
4
5
6
7
B 2 B 1 B 0
Working Principle of Octal to Binary Encoder: Say the switch of Octal number 2 is closed. 2 is connected only with OR
gate B . So a trigger applied makes B = 1 while B and B will retain their default value of 0. Thus B = 0 B = 1 and
1
1
2
2
1
0
B = 0 or 0 1 0 which is the binary equivalent of 2
0
Similarly on pressing switch 5 which is connected with B and B , we get B = 1 B = 0 and B = 1 or 1 0 1 which is the
2
0
0
1
2
binary equivalent of 5
2.4.2 Decimal to Binary Encoder
We know the base of a decimal number is 10 and the digits are from 0 to 9. We need 4 bits to represent the binary
value. So a binary encoder has 10 input lines and 4 output lines.
7474 Touchpad Computer Science-XII

