5-499
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).
C0049C0052 C0049C0051 C0049C0050 C0049C0049 C0049C0048 C0057
C0049 C0050 C0051 C0052 C0053 C0054 C0055
C0049C0054 C0049C0053
C0056
C0086
C0067C0067
C0052
C0069C0079 C0071C0083 C0051 C0050 C0048C0049
C0079C0085C0084C0080C0085C0084
C0065C0048
C0053 C0054 C0055 C0069C0073 C0065C0050 C0065C0049 C0071C0078C0068
C0079C0085C0084C0080C0085C0084C0083 C0073C0078C0080C0085C0084C0083
C0079C0085C0084C0080C0085C0084C0083C0073C0078C0080C0085C0084C0083
C0069C0079 C0071C0083 C0051 C0050 C0048C0049
C0053 C0054 C0055 C0069C0073 C0065C0050 C0065C0049
C0052 C0065C0048
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 H H H H H H H Z Z Z 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
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