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DM74LS251 3-STATE 1-of-8 Line Data Selector/Multiplexer
August 1986
Revised March 2000
DM74LS251
3-STATE 1-of-8 Line Data Selector/Multiplexer
General Description
These data selectors/multiplexers contain full on-chip
binary decoding to select one-of-eight data sources, and
feature a strobe-controlled 3-STATE output. The strobe
must be at a low logic level to enable these devices. The 3-
STATE outputs permit direct connection to a common bus.
When the strobe input is HIGH, both outputs are in a high-
impedance state in which both the upper and lower transis-
tors of each totem-pole output are OFF, and the output nei-
ther drives nor loads the bus significantly. When the strobe
is LOW, the outputs are activated and operate as standard
TTL totem-pole outputs.
To minimize the possibility that two outputs will attempt to
take a common bus to opposite logic levels, the output con-
trol circuitry is designed so that the average output disable
time is shorter than the average output enable time.
Features
s
3-STATE version of DM74LS151
s
Interface directly with system bus
s
Perform parallel-to-serial conversion
s
Permit multiplexing from N-lines to one line
s
Complementary outputs provide true and inverted data
s
Maximum number of common outputs: 129
s
Typical propagation delay time (D to Y): 17 ns
s
Typical power dissipation: 35 mW
Ordering Code:
Order Number
DM74LS251M
DM74LS251N
Package Number
M16A
N16E
Package Description
16-Lead Small Outline Integrated Circuit (SOIC), JEDEC MS-012, 0.150 Narrow
16-Lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300 Wide
Devices also available in Tape and Reel. Specify by appending the suffix letter “X” to the ordering code.
Connection Diagram
Function Table
Inputs
Select
C
X
L
L
L
L
H
H
H
H
B
X
L
L
H
H
L
L
H
H
A
X
L
H
L
H
L
H
L
H
Strobe
S
H
L
L
L
L
L
L
L
L
Outputs
Y
Z
D0
D1
D2
D3
D4
D5
D6
D7
W
Z
D0
D1
D2
D3
D4
D5
D6
D7
H
=
HIGH Logic Level
L
=
LOW Logic Level
X
=
Don't Care
Z
=
High Impedance (OFF)
D0, D1…D7
=
The level of the respective D input
© 2000 Fairchild Semiconductor Corporation
DS006415
www.fairchildsemi.com
DM74LS251
Logic Diagram
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2
DM74LS251
Absolute Maximum Ratings
(Note 1)
Supply Voltage
Input Voltage
Operating Free Air Temperature Range
Storage Temperature Range
7V
7V
0°C to
+70°C
−65°C
to
+150°C
Note 1:
The “Absolute Maximum Ratings” are those values beyond which
the safety of the device cannot be guaranteed. The device should not be
operated at these limits. The parametric values defined in the “Electrical
Characteristics” table are not guaranteed at the absolute maximum ratings.
The “Recommended Operating Conditions” table will define the conditions
for actual device operation.
Recommended Operating Conditions
Symbol
V
CC
V
IH
V
IL
I
OH
I
OL
T
A
Supply Voltage
HIGH Level Input Voltage
LOW Level Input Voltage
HIGH Level Output Current
LOW Level Output Current
Free Air Operating Temperature
0
Parameter
Min
4.75
2
0.8
−2.6
24
70
Nom
5
Max
5.25
Units
V
V
V
mA
mA
°C
Electrical Characteristics
over recommended operating free air temperature range (unless otherwise noted)
Symbol
V
I
V
OH
V
OL
Parameter
Input Clamp Voltage
HIGH Level
Output Voltage
LOW Level
Output Voltage
I
I
I
IH
I
IL
I
OZH
I
OZL
I
OS
I
CC1
I
CC2
Input Current @ Max Input Voltage
HIGH Level Input Current
LOW Level Input Current
Off-State Output Current with
HIGH Level Output Voltage Applied
Off-State Output Current with
LOW Level Output Voltage Applied
Short Circuit Output Current
Supply Current
Supply Current
Conditions
V
CC
=
Min, I
I
= −18
mA
V
CC
=
Min, I
OH
=
Max
V
IL
=
Max, V
IH
=
Min
V
CC
=
Min, I
OL
=
Max
V
IL
=
Max, V
IH
=
Min
I
OL
=
12 mA, V
CC
=
Min
V
CC
=
Max, V
I
=
7V
V
CC
=
Max, V
I
=
2.7V
V
CC
=
Max, V
I
=
0.4V
V
CC
=
Max, V
O
=
2.7V
V
IH
=
Min, V
IL
=
Max
V
CC
=
Max, V
O
=
0.4V
V
IH
=
Min, V
IL
=
Max
V
CC
=
Max (Note 3)
V
CC
=
Max (Note 4)
V
CC
=
Max (Note 5)
−20
6.1
7.1
2.4
3.1
0.35
0.25
0.5
0.4
0.1
20
−0.4
20
−20
−100
10
12
mA
µA
mA
µA
µA
mA
mA
mA
Min
Typ
(Note 2)
Max
−1.5
Units
V
V
V
Note 2:
All typicals are at V
CC
=
5V, T
A
=
25°C.
Note 3:
Not more than one output should be shorted at a time, and the duration should not exceed one second.
Note 4:
I
CC1
is measured with the outputs open, STROBE grounded, and all other inputs at 4.5V.
Note 5:
I
CC2
is measured with the outputs open and all inputs at 4.5V.
3
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DM74LS251
Switching Characteristics
at V
CC
=
5V and T
A
=
25°C
From (Input)
Symbol
Parameter
to (Output)
A, B, C
(4 Levels) to Y
A, B, C
(4 Levels) to Y
A, B, C
(3 Levels) to W
A, B, C
(3 Levels) to W
D to Y
D to Y
D to W
D to W
Strobe to Y
Strobe to Y
Strobe to Y
Strobe to Y
Strobe to W
Strobe to W
Strobe to W
Strobe to W
C
L
=
45 pF
Min
t
PLH
t
PHL
t
PLH
t
PHL
t
PLH
t
PHL
t
PLH
t
PHL
t
PZH
t
PZL
t
PHZ
t
PLZ
t
PZH
t
PZL
t
PHZ
t
PLZ
Propagation Delay Time
LOW-to-HIGH Level Output
Propagation Delay Time
HIGH-to-LOW Level Output
Propagation Delay Time
LOW-to-HIGH Level Output
Propagation Delay Time
HIGH-to-LOW Level Output
Propagation Delay Time
LOW-to-HIGH Level Output
Propagation Delay Time
HIGH-to-LOW Level Output
Propagation Delay Time
LOW-to-HIGH Level Output
Propagation Delay Time
HIGH-to-LOW Level Output
Output Enable Time to
HIGH Level Output
Output Enable Time to
LOW Level Output
Output Disable Time from
HIGH Level Output (Note 6)
Output Disable Time from
LOW Level Output (Note 6)
Output Enable Time to
HIGH Level Output
Output Enable Time to
LOW Level Output
Output Disable Time from
HIGH Level Output (Note 6)
Output Disable Time from
LOW Level Output (Note 6)
Note 6:
C
L
=
5 pF
R
L
=
667Ω
C
L
=
150 pF
Min
Max
53
53
38
42
35
38
25
25
60
51
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
ns
40
47
ns
ns
ns
ns
Units
Max
45
45
33
33
28
28
15
15
45
40
45
25
27
40
55
25
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