Digital Circuits & Design, 1st Education by Pearson

6.26 | Chapter 6

6.3.6 | Decimal-to-BCD Priority Encoder

An encoder is a combinational logic function that has 10 (<2

n

) input lines and 4 output

lines. The 4 output lines generate the BCD code for the possible 10 decimal input lines.

A priority is assigned to each input so that, when more than one input is simultaneously

active, the input with the highest priority is encoded. The truth table of decimal-to-BCD

priority encoder is given in Table 6.15.

TABLE 6.15 | Decimal-to-BCD Priority encoder

Decimal

Value

Input Output

I

9

I

8

I

7

I

6

I

5

I

4

I

3

I

2

I

1

I

0

b

3

b

2

b

1

b

0

0 0 0 0 0 0 0 0 0 0 1 0 0 0 0

1 0 0 0 0 0 0 0 0 1 X 0 0 0 1

2 0 0 0 0 0 0 0 1 X X 0 0 1 0

3 0 0