5-1
FAST AND LS TTL DATA
8-INPUT PRIORITY ENCODERS
WITH 3-STATE OUTPUTS
The SN54/74LS348 and the SN54/74LS848 are eight input priority encod-
ers which provide the 8-line to 3-line function.
The outputs (A0–A2) and inputs (0–7) are active low . The active low input
which has the highest priority (input 7 has the highest) is represented on the
outputs (output A0 is the lowest bit). An example would be if inputs 1, 2 and 4
were low, then a binary 4 would be represented on the outputs.
The GS (Group Signal) output is active low when any of the inputs are low. It
serves to indicate when any of the inputs are active.
A0, A1 and A2 are three-state outputs. This allows for up to 64 line expan-
sion without the need for special external circuitry.
A logical one on the Enable Input (EI) forces A0, A1 ared A2 to the disabled
state and outputs GS and EO to the high state. A high on all data inputs (0–7)
together with a low on the EI input disables outputs A0, A1, and A2 and forces
output GS to the high state and output EO to the low state.
Use of the EI input in conjunction with the EO output provides for the capa-
bility of having priority encoding of n input signals.
The LS848 has special internal circuitry providing for a greatly reduced neg-
ative going glitch on the GS (Group Signal) output and on a reduced tendency
for the A0, A1 and A2 outputs to become momentarily enabled. Both of these
occurrences happen when the EI input goes from a logical one to a logical zero
and all data inputs (0–7) are held at logical ones. The internal glitch reduction
circuitry does add an additional fan-in of one on all data inputs (compared to
that of the LS348).
14 13 12 11 10 9
1234567
16 15
8
VCC
4
EO GS 3 2 01 OUTPUT
A0
5 6 7 EI A2 A1 GND
OUTPUTS INPUTS
OUTPUTSINPUTS
EO GS 3 2 01
567EIA2A1
4A0
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 Z Z Z H H
L H HHHHHHH Z ZZHL
LXXXXXXXL L LLLH
LXXXXXXLH L LHLH
LXXXXXLHH L HLLH
LXXXXLHHH L HHL H
LXXXLHHHH H LLLH
LXXLHHHHH H LHLH
LXLHHHHHH H HLLH
LLHHHHHHHHHHLH
SN54/74LS348
SN54/74LS848
8-INPUT PRIORITY ENCODERS
WITH 3-STATE OUTPUTS
LOW POWER SCHOTTKY
ORDERING INFORMATION
SN54LSXXXJ Ceramic
SN74LSXXXN Plastic
SN74LSXXXD SOIC
J SUFFIX
CERAMIC
CASE 620-09
N SUFFIX
PLASTIC
CASE 648-08
16 1
16
1
16 1
D SUFFIX
SOIC
CASE 751B-03
H = HIGH Logic Level
L = LOW Logic Level
X = Irrelevant
Z = High Impedance State
5-2
FAST AND LS TTL DATA
SN54/74LS348 • SN54/74LS848
BLOCK DIAGRAMS
SN54/74LS348 SN54/74LS848
EI
0
1
2
3
4
5
6
7
(5)
(10)
(11)
(12)
(13)
(1)
(2)
(3)
(4)
EO
GS
A0
A1
A2
(15)
(14)
(9)
(7)
(6)
EI
0
1
2
3
4
5
6
7
(5)
(10)
(11)
(12)
(13)
(1)
(2)
(3)
(4)
EO
GS
A0
A1
A2
(15)
(14)
(9)
(7)
(6)
G1
″
G2
′
G3
′
G4
′
G5
′
G6
′
G7
′
G8
′
G9
′
G10
′
G11
′
G12
′
G31
G13
G14
G15
G16
G17
G18
G19
G20
G21
G22
G24
G25
G26
G27
G29
G30
G23
G28
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
TAOperating Ambient Temperature Range 54
74 –55
025
25 125
70 °C
IOH Output Current — High EO, GS 54, 74 –0.4 mA
IOH Output Current — High A0, A1, A2
A0, A1, A2 54
74 –1.0
–2.6 mA
IOL Output Current — Low EO, GS 54
74 4.0
8.0 mA
IOL Output Current — Low A0, A1, A2
A0, A1, A2 54
74 12
24 mA
5-3
FAST AND LS TTL DATA
SN54/74LS348 • SN54/74LS848
DC CHARACTERISTICS OVER OPERATING TEMPERATURE RANGE (unless otherwise specified)
Sbl
P
Limits
Ui
T C di i
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
V
IL
I
npu
t
LOW
V
o
lt
age 74 0.8
V
pg
All Inputs
VIK Input Clamp Diode Voltage –0.65 –1.5 V VCC = MIN, IIN = –18 mA
V
Output HIGH Voltage
A0, A1, A2 54, 74 2.4 3.1 V V
CC
= MIN
,
I
OH
= MAX
,
V
IN
= V
IH
VOH EO, GS 54 2.5 3.5 V
VCC
=
MIN
,
IOH
=
MAX
,
VIN
=
VIH
or VIL per T ruth Table
EO, GS 74 2.7 3.5 V
VOL
Output LOW Voltage 54, 74 0.25 0.4 V IOL = 4.0 mA VCC = VCC MIN,
VIN =V
IL or VIH
V
OL
pg
EO, GS 74 0.35 0.5 V IOL = 8.0 mA
V
IN =
V
IL or
V
IH
per T ruth Table
VOL
Output LOW Voltage 54, 74 0.25 0.4 V IOL = 12 mA VCC = VCC MIN,
VIN =V
IL or VIH
V
OL
pg
A0, A1, A2 74 0.35 0.5 V IOL = 24 mA
V
IN =
V
IL or
V
IH
per T ruth Table
IOZH Output Off Current HIGH 20 µA VCC = MAX, VOUT = 2.7 V
IOZL Output Off Current LOW –20 µA VCC = MAX, VOUT = 0.4 V
I
Input HIGH Current
Input 0, EI — LS348 20 µA
V MAX V 2 7 V
I
Input 0 — LS848 40 µAVCC = MAX, VIN = 2.7 V
IIH
Other — LS348
Other — LS848 40
60 µA
µA
I
IH Input HIGH Current
Input 0, EI — LS348 0.1 mA
V MAX V 7 0 V
Input 0 — LS848 0.2 mA VCC = MAX, VIN = 7.0 V
Other — LS348
Other — LS848 0.2
0.3 mA
mA
I
Input LOW Current
Input 0, EI — LS348 –0.4 mA
V MAX V 0 4 V
IIL Input 0 — LS848 –0.8 mA VCC = MAX, VIN = 0.4 V
Other — LS348
Other — LS848 –0.8
–1.2 mA
mA
IOS Short Circuit Current (Note 1)
EO, GS –20 –120 mA VCC = MAX
OS
,
A0, A1, A2 –30 –130 mA
CC
ICC
Power Supply Current
Total, Output HIGH 12 23
mA
VCC = MAX
All Inputs and Outputs Open
I
CC Total, Output LOW 13 25 m
A
VCC = MAX, Inputs 7, EI = GND
All Others Open
Note 1: Not more than one output should be shorted at a time, nor for more than 1 second.
5-4
FAST AND LS TTL DATA
SN54/74LS348 • SN54/74LS848
AC CHARACTERISTICS (VCC = 5.0 V, T A = 25°C)
Sbl
From To
Wf
LS348
Limits LS848
Limits
T C di i
Symbol
From
(Input)
To
(Output) Waveform Min Typ Max Min Typ Max Unit Test Conditions
tPLH
1 thru 7
A0 A1 or A2
In-Phase 11 17 12 18
C45F
tPHL
1
th
ru
7
A0
,
A1
or
A2
output 20 30 20 30 ns
C45F
tPLH
1 thru 7
A0 A1 or A2
Out-of-Phase 23 35 23 35
CL = 45 pF
tPHL
1
th
ru
7
A0
,
A1
or
A2
output 23 35 23 35 ns
Lp
RL = 667 Ω
tPZH
EI
A0 A1 or A2
25 39 25 39
tPZL
EI
A0
,
A1
or
A2
24 41 24 41 ns
tPLH
0 thru 7
E0
Out-of-Phase 11 18 11 18
C15F
tPHL
0
th
ru
7
E0
output 26 40 26 40 ns
C15F
tPLH
0 thru 7
GS
In-Phase 38 55 38 55
C15F
tPHL
0
th
ru
7
GS
output 9.0 21 9.0 21 ns CL = 15 pF
tPLH
EI
GS
In-Phase 11 17 11 17
Lp
RL = 2.0 Ω
tPHL
EI
GS
output 14 36 14 36 ns
tPLH
EI
EO
In-Phase 17 21 17 21
tPHL
EI
EO
output 25 40 30 45 ns
tPHZ
EI
A0 A1 or A2
18 27 18 27
CL = 5.0 pF
tPLZ
EI
A0
,
A1
or
A2
23 35 23 35 ns
Lp
RL = 667 Ω