74F253 View Datasheet(PDF) - Fairchild Semiconductor
Part Name
Description
View to exact match
74F253 Datasheet PDF : 7 Pages
| |||
Unit Loading/Fan Out
Pin Names
Description
I0a–I3a
I0b–I3b
S0–S1
OEa
OEb
Za, Zb
Side A Data Inputs
Side B Data Inputs
Common Select Inputs
Side A Output Enable Input (Active LOW)
Side B Output Enable Input (Active LOW)
3-STATE Outputs
U.L.
HIGH/LOW
1.0/1.0
1.0/1.0
1.0/1.0
1.0/1.0
1.0/1.0
150/40(33.3)
Input IIH/IIL
Output IOH/IOL
20 µA/−0.6 mA
20 µA/−0.6 mA
20 µA/−0.6 mA
20 µA/−0.6 mA
20 µA/−0.6 mA
−3 mA/24 mA (20 mA)
Functional Description
This device contains two identical 4-input multiplexers with
3-STATE outputs. They select two bits from four sources
selected by common Select inputs (S0, S1). The 4-input
multiplexers have individual Output Enable (OEa, OEb)
inputs which, when HIGH, force the outputs to a high
impedance (High Z) state. This device is the logic imple-
mentation of a 2-pole, 4-position switch, where the position
of the switch is determined by the logic levels supplied to
the two select inputs. The logic equations for the outputs
are shown below:
Za = OEa • (I0a • S1 • S0 + I1a • S1 • S0 +
I2a • S1 • S0 + I3a • S1 • S0)
Zb = OEb • (I0b • S1 • S0 + I1b • S1 • S0 +
I2b • S1 • S0 + I3b • S1 • S0)
If the outputs of 3-STATE devices are tied together, all but
one device must be in the high impedance state to avoid
high currents that would exceed the maximum ratings.
Designers should ensure that Output Enable signals to
3-STATE devices whose outputs are tied together are
designed so that there is no overlap.
Truth Table
Select
Inputs
S0 S1
XX
LL
LL
HL
Data Inputs
I0 I1 I2 I3
XXXX
LXXX
HXXX
XLXX
Output
Enable
OE
H
L
L
L
Output
Z
Z
L
H
L
HL XHXX
L
H
L HXX L X
L
L
LHXXHX
L
H
HHXXX L
L
L
HHXXXH
L
H
Address inputs S0 and S1 are common to both sections.
H = HIGH Voltage Level
L = LOW Voltage Level
X = Immaterial
Z = High Impedance
Logic Diagram
Please note that this diagram is provided only for the understanding of logic operations and should not be used to estimate propagation delays.
www.fairchildsemi.com
2
|
|
Share Link: 