M74HCT646 STMICROELECTRONICS [STMicroelectronics], M74HCT646 Datasheet - Page 3

• Manufacturer Part Number: M74HCT646
• Description: HCT646 OCTAL BUS TRANSCEIVER/REGISTER 3-STATE HCT648 OCTAL BUS TRANSCEIVER/REGISTER 3-STATE, INV.
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

TRUTH TABLE
HCT646 (The truth table for HCT648 is the same as this, but with the outputs inverted)
X
Z
Qn
*
G
H
L
L
: THE DATA AT THE A AND B BUS WILL BE STORED TO THE INTERNAL FLIP-FLOPS ON EVERY LOW TO HIGH TRANSITION OF
THE CLOCK INPUTS
: DON’T CARE
: HIGH IMPEDANCE
: THE DATA STORED TO THE INTERNAL FLIP-FLOPS BY MOST RECENT LOW TO HIGH TRANSITION OF THE CLOCK INPUTS
DIR CAB CBA SAB SBA
H
X
L
X*
X*
X*
x*
X
X
X
X*
X*
X*
X*
X
X
X
X
X
H
H
X
X
X
X
L
L
H
H
X
X
X
X
X
X
L
L
OUTPUTS
INPUTS
INPUTS
iNPUTS
Qn
A
Z
H
H
X
H
L
L
L
L
H
L
H
L
H
OUTPUTS
INPUTS
INPUTS
INPUTS
Qn
B
H
H
H
H
H
H
Z
X
L
L
L
L
L
L
Both the A bus and the B bus are inputs
The output functions of the A and B bus are disabled
Both the A and B bus are used for inputs to the
internal flip-flops. Data at the bus will be stored on
low to high transition of the clock inputs
The A bus are inputs and the B bus are outputs
The data at the A bus are displayed at the B bus
The data at the A bus are displayed at the B bus.
The data of the A bus are stored to the internal
flip-flop on low to high transition of th clock pulse.
The data stored to the internal flip-flop are dispayed
at the B bus
The data at the A bus are stored to the internal flip-
flop on low to high transition of the clock pulse. The
states of the internal flip-flops output directly to the
B bus
The A bus are outputs and the B bus are inputs
The data at the B bus are displayed at the A bus
The data at the B bus are displayed at the A bus.
The data of the B bus are stored to the internal flip-
flop on low to high transition of the clock pulse
The data stored to the internal flip-flops are
displayed at the B bus
the data at the B bus are stored to the internal flip-
flop on low to high transition of the clock pulse. The
states of the internal flip-flops output directly to the
A bus
FUNCTION
M74HCT646/648
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