參數(shù)資料
型號: 74F257ASC
廠商: FAIRCHILD SEMICONDUCTOR CORP
元件分類: 通用總線功能
英文描述: Quad 2-Input Multiplexer with 3-STATE Outputs
中文描述: F/FAST SERIES, QUAD 2 LINE TO 1 LINE MULTIPLEXER, TRUE OUTPUT, PDSO16
封裝: 0.150 INCH, MS-012, SOIC-16
文件頁數(shù): 2/8頁
文件大?。?/td> 157K
代理商: 74F257ASC
Unit Loading/Fan Out
54F/74F
Pin Names
Description
U.L.
Input I
IH
/I
IL
Output I
OH
/I
OL
HIGH/LOW
S
OE
I
0a
–I
0d
I
1a
–I
1d
Z
a
–Z
d
Common Data Select Input
TRI-STATE Output Enable Input (Active LOW)
Data Inputs from Source 0
Data Inputs from Source 1
TRI-STATE Multiplexer Outputs
1.0/1.0
1.0/1.0
1.0/1.0
1.0/1.0
150/40 (33.3)
20
m
A/
b
0.6 mA
20
m
A/
b
0.6 mA
20
m
A/
b
0.6 mA
20
m
A/
b
0.6 mA
b
3 mA/24 mA (20 mA)
Functional Description
The ’F257A is a quad 2-input multiplexer with TRI-STATE
outputs. It selects four bits of data from two sources under
control of a Common Data Select input. When the Select
input is LOW, the I
0x
inputs are selected and when Select is
HIGH, the I
1x
inputs are selected. The data on the selected
inputs appears at the outputs in true (non-inverted) form.
The device is the logic implementation of a 4-pole, 2-posi-
tion switch where the position of the switch is determined by
the logic levels supplied to the Select input. The logic equa-
tion for the outputs is shown below:
Z
n
e
OE
#
(I
n
#
S
a
I
on
#
S)
When the Output Enable input (OE) is HIGH, the outputs are
forced to a high impedance OFF state. If the outputs are
tied together, all but one device must be in the high imped-
ance state to avoid high currents that would exceed the
maximum ratings. Designers should ensure the Output En-
able signals to TRI-STATE devices whose outputs are tied
together are designed so there is no overlap.
Truth Table
Output
Enable
Select
Input
Data
Inputs
Output
OE
S
I
0
I
1
Z
H
L
L
L
L
X
H
H
L
L
X
X
X
L
H
X
L
H
X
X
Z
L
H
L
H
H
e
HIGH Voltage Level
L
e
LOW Voltage Level
X
e
Immaterial
Z
e
High Impedance
TL/F/9507–4
Please note that this diagram is provided only for the understanding of logic operations and should not be used to estimate propagation delays.
2
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