HD74HC149
8-to-8-line Priority Encoder
Description
The HD74HC149 is priority encoder which has 8 input lines (0 - 7) and 8 output lies (Y
0
- Y
7
).
It is the logical combination of a HD74HC148 8-3 line priority encoder driving a HD74HC138 3-8 line
decoder.
Only one request output can be low at a time. The output that is low is dependent on the highest priority
request that is low. The order of priority is 7 highest and 0 lowest.
When
E input is high, all outputs are high.
When a output (Y
0
- Y
7
) is low,
P output is low and this indicates active condition.
Features
·
High Speed Operation: t
pd
(0 - 7 to Y) = 16 ns typ (C
L
= 50 pF)
·
High Output Current: Fanout of 10 LSTTL Loads
·
Wide Operating Voltage: V
CC
= 2 to 6 V
·
Low Input Current: 1 µA max
·
Low Quiescent Supply Current: I
CC
(static) = 4 µA max (Ta = 25°C)