Multiplexers and Demultiplexers
283
Table 8.9 Priority encoder.
D 0
D 1
D 2
D 3
D 4
D 5
D 6
D 7
A
B
C
1
0
0
0
0
0
0
0
0
0
0
X
1
0
0
0
0
0
0
0
0
1
X
X
1
0
0
0
0
0
0
1
0
X
X
X
1
0
0
0
0
0
1
1
X
X
X
X
1
0
0
0
1
0
0
X
X
X
X
X
1
0
0
1
0
1
X
X
X
X
X
X
1
0
1
1
0
X
X
X
X
X
X
X
1
1
1
1
Figure 8.16 10-line decimal to four-line BCD priority encoder.
Some of the encoders available in IC form provide additional inputs and outputs to allow expansion.
IC 74148, which is an eight-line to three -line priority encoder, is an example. ENABLE-IN (EI) and
ENABLE-OUT (EO) terminals on this IC allow expansion. For instance, two 74148s can be cascaded
to build a 16-line to four-line priority encoder.