MC74LCX646
TRUTH TABLE
OE
DIR
Inputs
CAB
CBA
SAB
SBA
Data Ports
An
Bn
Operating Mode
H
X
↑
↑
Input
Input
↑
X
X
X
X
Isolation, Hold Storage
↑
X
X
l
h
X
X
X
Store A and/or B Data
X
l
h
L
H
↑
Input
Output
X*
L
X
L
H
L
Real Time A Data to B Bus
H
H
X
X
↑
X*
L
X
l
h
QA
Stored A Data to B Bus
L
Real Time A Data to B Bus; Store A
H
Data
H
X
L
H
QA
Clock A Data to B Bus; Store A Data
QA
L
L
Output
Input
X*
↑
X
L
L
H
L
Real Time B Data to A Bus
H
X
H
QB
X*
↑
X
L
L
H
X
Stored B Data to A Bus
l
Real Time B Data to A Bus; Store B
h
Data
X
H
QB
QB
L
Clock B Data to A Bus; Store B Data
H
H = High Voltage Level
h = High Voltage Level One Setup Time Prior to the Low−to−High Clock Transition
L = Low Voltage Level
l = Low Voltage Level One Setup Time Prior to the Low−to−High Clock Transition
X = Don’t Care
↑ = Low−to−High Clock Transition
↑ = NOT Low−to−High Clock Transition
QA = A input storage register
QB = B input storage register
* = The clocks are not internally gated with either the Output Enables or the Source Inputs. Therefore, data at the A or B ports may be
clocked into the storage registers, at any time. For ICC reasons, Do Not Float Inputs.
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