Page 60 - Digital Electronics by harish

2.9 Encoder

An encoder is a code converter circuit which is used to convert an active input signal to a
coded output signal. This is shown in figure. It should be noted that encoders have more
number of input lines and less number of output lines.

There are „n‟ input signals, only one of which is active. The encoder circuit converts this
active input to „m‟ bit coded output (n > m). Decimal to BCD converter is a good example for
encoder.

Decimal to BCD encoder

The logic diagram of Decimal to BCD encoder is shown in figure.

There are 10 input switches corresponding to ten decimal numbers 0, 1, 2, 3, 4, 5, 6, 7, 8 and
9. The BCD outputs are taken from the OR gates. When any one of the input switches is
pressed, the corresponding output will be generated in BCD form. The truth table is shown in
figure.

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