74ABT646 Fairchild Semiconductor, 74ABT646 Datasheet - Page 2

• Manufacturer Part Number: 74ABT646
• Description: Octal Transceivers and Registers with 3-STATE Outputs
• Manufacturer: Fairchild Semiconductor

www.fairchildsemi.com
Truth Table
H
L

X
Note 1: The data output functions may be enabled or disabled by various signals at the OE and DIR inputs. Data input functions are always enabled;
i.e., data at the bus pins will be stored on every LOW-to-HIGH transition of the appropriate clock inputs.
LOW Voltage Level
HIGH Voltage Level
Immaterial
OE
LOW-to-HIGH Transition
H
H
H
L
L
L
L
L
L
L
L
DIR
X
X
X
H
H
H
H
L
L
L
L
Real Time Transfer
Real Time Transfer
CPAB
H or L
H or L
A-Bus to B-Bus
B-Bus to A-Bus



X
X
X
X
X
X
FIGURE 1.
FIGURE 2.
Inputs
CPBA
H or L
H or L



X
X
X
X
X
X
SAB
X
X
X
H
H
X
X
X
X
L
L
SBA
X
X
X
X
X
X
X
H
H
L
L
Output
A
Input
Input
0
–A
(Note 1)
Data I/O
2
7
Output Clock A
B
Input
Input
0
–B
7
Isolation
Clock A
Clock B
A
A Register to B
Clock A
B
Clock B
B Register to A
Clock B
n
n
to B
to A
n
n
n
n
n
n
n
n
—Real Time (Transparent Mode)
—Real Time (Transparent Mode)
Data into A Register
Data into B Register
Data into A Register
Data into A Register and Output to B
Data into B Register
Data into B Register and Output to A
Bus to Register
Register to Bus
Transfer from
Storage from
FIGURE 3.
FIGURE 4.
n
n
(Stored Mode)
(Stored Mode)
Function
n
n