5-245
FAST AND LS TTL DATA
10-LINE-TO-4-LINE
AND 8-LINE-TO-3-LINE
PRIORITY ENCODERS
The SN54 / 74LS147 and the SN54/ 74LS148 are Priority Encoders. They
provide priority decoding of the inputs to ensure that only the highest order
data line is encoded. Both devices have data inputs and outputs which are
active at the low logic level.
The LS147 encodes nine data lines to four-line (8-4-2-1) BCD. The implied
decimal zero condition does not require an input condition because zero is
encoded when all nine data lines are at a high logic level.
The LS148 encodes eight data lines to three-line (4-2-1) binary (octal). By
providing cascading circuitry (Enable Input EI and Enable Output EO) octal
expansion is allowed without needing external circuitry.
The SN54 / 74LS748 is a proprietary Motorola part incorporating a built-in
deglitcher network which minimizes glitches on the GS output. The glitch
occurs on the negative going transition of the EI input when data inputs 0 7
are at logical ones.
The only dc parameter differences between the LS148 and the LS748 are
that (1) Pin 10 (input 0) has a fan-in of 2 on the LS748 versus a fan-in of 1 on
the LS148; (2) Pins 1, 2, 3, 4, 11, 12 and 13 (inputs 1, 2, 3, 4, 5, 6, 7) have a
fan-in of 3 on the LS748 versus a fan-in of 2 on the LS148.
The only ac difference is that tPHL from EI to EO is changed from 40 to
45 ns.
SN54 / 74LS147
(TOP VIEW)
SN54 / 74LS148
SN54 / 74LS748
(TOP VIEW)
4
5
6
7
8
C
B
GND
D
3
2
1
9
A
VCC NC
14
13
12
11
10
9
1
2
3
4
5
6
7
16
15
8
D
3
2
1
9
A
4
5
6
7
8
C
B
OUTPUT
INPUTS
OUTPUT
INPUTS
OUTPUTS
4
5
6
7
E1
A2
A1 GND
VCC EO GS
3
2
1
0
A0
14
13
12
11
10
9
1
2
3
4
5
6
7
16
15
8
EO
GS
3
2
1
0
A0
4
5
6
7
EI
A2
A1
OUTPUTS
INPUTS
OUTPUT
INPUTS
OUTPUTS
SN54/74LS147
SN54/74LS148
SN54/74LS748
10-LINE-TO-4-LINE
AND 8-LINE-TO-3-LINE
PRIORITY ENCODERS
LOW POWER SCHOTTKY
J SUFFIX
CERAMIC
CASE 620-09
N SUFFIX
PLASTIC
CASE 648-08
16
1
16
1
ORDERING INFORMATION
SN54LSXXXJ
Ceramic
SN74LSXXXN
Plastic
SN74LSXXXD
SOIC
16
1
D SUFFIX
SOIC
CASE 751B-03
5-246
FAST AND LS TTL DATA
SN54/74LS147
SN54/74LS148
SN54/74LS748
SN54 / 74LS147
FUNCTION TABLE
INPUTS
OUTPUTS
1
2
3
4
5
6
7
8
9
D
C
B
A
H
H
H
H
H
H
H
H
H
H
H
H
H
X
X
X
X
X
X
X
X
L
L
H
H
L
X
X
X
X
X
X
X
L
H
L
H
H
H
X
X
X
X
X
X
L
H
H
H
L
L
L
X
X
X
X
X
L
H
H
H
H
L
L
H
X
X
X
X
L
H
H
H
H
H
L
H
L
X
X
X
L
H
H
H
H
H
H
L
H
H
X
X
L
H
H
H
H
H
H
H
H
L
L
X
L
H
H
H
H
H
H
H
H
H
L
H
L
H
H
H
H
H
H
H
H
H
H
H
L
SN54 / 74LS148
SN54 / 74LS748
FUNCTION TABLE
INPUTS
OUTPUTS
EI
0
1
2
3
4
5
6
7
A2
A1
A0
GS
EO
H
X
X
X
X
X
X
X
X
H
H
H
H
H
L
H
H
H
H
H
H
H
H
H
H
H
H
L
L
X
X
X
X
X
X
X
L
L
L
L
L
H
L
X
X
X
X
X
X
L
H
L
L
H
L
H
L
X
X
X
X
X
L
H
H
L
H
L
L
H
L
X
X
X
X
L
H
H
H
L
H
H
L
H
L
X
X
X
L
H
H
H
H
H
L
L
L
H
L
X
X
L
H
H
H
H
H
H
L
H
L
H
L
X
L
H
H
H
H
H
H
H
H
L
L
H
L
L
H
H
H
H
H
H
H
H
H
H
L
H
H = HIGH Logic Level, L = LOW Logic Level, X = Irrelevant
FUNCTIONAL BLOCK DIAGRAMS
SN54 / 74LS147
SN54 / 74LS148
1
2
3
4
5
6
7
8
9
(11)
(12)
(13)
(1)
(2)
(3)
(4)
(5)
(10)
(9)
(7)
(6)
(14)
A
B
C
D
0
1
2
3
4
5
6
7
EI
(10)
(11)
(12)
(13)
(1)
(2)
(3)
(4)
(5)
(15)
EO
(14)
GS
(8)
A0
(7)
A1
(6)
A2
5-248
FAST AND LS TTL DATA
SN54/74LS147
SN54/74LS148
SN54/74LS748
GUARANTEED OPERATING RANGES
Symbol
Parameter
Min
Typ
Max
Unit
VCC
Supply Voltage
54
74
4.5
4.75
5.0
5.0
5.5
5.25
V
TA
Operating Ambient Temperature Range
54
74
55
0
25
25
125
70
C
IOH
Output Current -- High
54, 74
0.4
mA
IOL
Output Current -- Low
54
74
4.0
8.0
mA
DC CHARACTERISTICS OVER OPERATING TEMPERATURE RANGE
(unless otherwise specified)
Symbol
Parameter
Limits
Unit
Test Conditions
Symbol
Parameter
Min
Typ
Max
Unit
Test Conditions
VIH
Input HIGH Voltage
2.0
V
Guaranteed Input HIGH Voltage for
All Inputs
VIL
Input LOW Voltage
54
0.7
V
Guaranteed Input LOW Voltage for
All Inputs
VIL
Input LOW Voltage
74
0.8
V
Guaranteed Input LOW Voltage for
All Inputs
VIK
Input Clamp Diode Voltage
0.65
1.5
V
VCC = MIN, IIN = 18 mA
VOH
Output HIGH Voltage
54
2.5
3.5
V
VCC = MIN, IOH = MAX, VIN = VIH
or VIL per Truth Table
VOH
Output HIGH Voltage
74
2.7
3.5
V
VCC = MIN, IOH = MAX, VIN = VIH
or VIL per Truth Table
VOL
Output LOW Voltage
54, 74
0.25
0.4
V
IOL = 4.0 mA
VCC = VCC MIN,
VIN = VIL or VIH
per Truth Table
VOL
Output LOW Voltage
74
0.35
0.5
V
IOL = 8.0 mA
VIN = VIL or VIH
per Truth Table
IIH
Input HIGH Current
All Others
Input 0 (LS748)
Inputs 1 7 (LS148)
Inputs 1 7 (LS748)
20
40
40
60
A
VCC = MAX, VIN = 2.7 V
IIH
All Others
Input 0 (LS748)
Inputs 1 7 (LS148)
Inputs 1 7 (LS748)
0.1
0.2
0.2
0.3
mA
VCC = MAX, VIN = 7.0 V
IIL
Input LOW Current
All Others
Input 0 (LS748)
Inputs 1 7 (LS148)
Inputs 1 7 (LS748)
0.4
0.8
0.8
1.2
mA
VCC = MAX, VIN = 0.4 V
IOS
Short Circuit Current (Note 1)
20
100
mA
VCC = MAX
ICCH
Power Supply Current Output HIGH
17
mA
VCC = MAX, All Inputs = 4.5 V
ICCL
Output LOW
20
mA
VCC = MAX, Inputs 7 & E1 = GND
All Other Inputs = 4.5 V
Note 1: Not more than one output should be shorted at a time, nor for more than 1 second.
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