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Part Number HD74HC149

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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)
HD74HC149
2
Function Table
Inputs
Outputs
0
1
2
3
4
5
6
7
E
Y
0
Y
1
Y
2
Y
3
Y
4
Y
5
Y
6
Y
7
P
X
X
X
X
X
X
X
X
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
L
H
H
H
H
H
H
H
H
H
X
X
X
X
X
X
X
L
L
H
H
H
H
H
H
H
L
L
X
X
X
X
X
X
L
H
L
H
H
H
H
H
H
L
H
L
X
X
X
X
X
L
H
H
L
H
H
H
H
H
L
H
H
L
X
X
X
X
L
H
H
H
L
H
H
H
H
L
H
H
H
L
X
X
X
L
H
H
H
H
L
H
H
H
L
H
H
H
H
L
X
X
L
H
H
H
H
H
L
H
H
L
H
H
H
H
H
L
X
L
H
H
H
H
H
H
L
H
L
H
H
H
H
H
H
L
L
H
H
H
H
H
H
H
L
L
H
H
H
H
H
H
H
L
H :
High level
L
:
Low level
X :
Irrelevant
Pin Arrangement
1
2
3
4
5
6
7
8
9
10
0
1
2
3
4
5
6
7
E
GND
20
19
18
17
16
15
14
13
12
11
V
CC
Y
0
Y
1
Y
2
Y
3
Y
4
Y
5
Y
6
Y
7
P
(Top view)
Inputs
Outputs
HD74HC149
3
Logic Diagram
0
E
P
Y
0
Y
1
Y
2
Y
3
Y
4
Y
5
Y
6
Y
7
1
2
3
4
5
6
7
HD74HC149
4
DC Characteristics
Ta = 25
°
C
Ta = ­40 to
+85
°
C
Item
Symbol
V
CC
(V) Min Typ Max Min
Max
Unit
Test Conditions
Input voltage
V
IH
2.0
1.5
--
--
1.5
--
V
4.5
3.15 --
--
3.15
--
6.0
4.2
--
--
4.2
--
V
IL
2.0
--
--
0.5
--
0.5
V
4.5
--
--
1.35 --
1.35
6.0
--
--
1.8
--
1.8
Output voltage
V
OH
2.0
1.9
2.0
--
1.9
--
V
Vin = V
IH
or V
IL
I
OH
= ­20
µ
A
4.5
4.4
4.5
--
4.4
--
6.0
5.9
6.0
--
5.9
--
4.5
4.18 --
--
4.13
--
I
OH
= ­4 mA
6.0
5.68 --
--
5.63
--
I
OH
= ­5.2 mA
V
OL
2.0
--
0.0
0.1
--
0.1
V
Vin = V
IH
or V
IL
I
OL
= 20
µ
A
4.5
--
0.0
0.1
--
0.1
6.0
--
0.0
0.1
--
0.1
4.5
--
--
0.26 --
0.33
I
OL
= 4 mA
6.0
--
--
0.26 --
0.33
I
OL
= 5.2 mA
Input current
Iin
6.0
--
--
±
0.1 --
±
1.0
µ
A
Vin = V
CC
or GND
Quiescent supply
current
I
CC
6.0
--
--
4.0
--
40
µ
A
Vin = V
CC
or GND, Iout = 0
µ
A
HD74HC149
5
AC Characteristics (C
L
= 50 pF, Input t
r
= t
f
= 6 ns)
Ta = 25
°
C
Ta = ­40 to
+85
°
C
Item
Symbol
V
CC
(V) Min Typ Max Min
Max
Unit
Test Conditions
Propagation delay t
PLH
2.0
--
--
140 --
175
ns
0 - 7 to Y,
P
time
t
PHL
4.5
--
16
28
--
35
6.0
--
--
24
--
30
t
PLH
2.0
--
--
155 --
195
ns
E
to Y,
P
t
PHL
4.5
--
13
31
--
39
6.0
--
--
26
--
33
Output rise/fall
t
TLH
2.0
--
--
75
--
95
ns
time
t
THL
4.5
--
5
15
--
19
6.0
--
--
13
--
16
Input capacitance
Cin
--
--
5
10
--
10
pF