SN54LVTH646, SN74LVTH646

3.3-V ABT OCTAL BUS TRANSCEIVERS AND REGISTERS

WITH 3-STATE OUTPUTS

SCBS705E – AUGUST 1997 – REVISED APRIL 1999

2

POST OFFICE BOX 655303

description (continued)

When an output function is disabled, the input function is still enabled and can be used to store and transmit

data. Only one of the two buses, A or B, can be driven at a time.

Active bus-hold circuitry is provided to hold unused or floating data inputs at a valid logic level.

the minimum value of the resistor is determined by the current-sinking capability of the driver.

disables the outputs, preventing damaging current backflow through the devices when they are powered down.

The power-up 3-state circuitry places the outputs in the high-impedance state during power up and power down,

which prevents driver conflict.

The SN54LVTH646 is characterized for operation over the full military temperature range of –55

°C to 125°C.

The SN74LVTH646 is characterized for operation from –40

°C to 85°C.

FUNCTION TABLE

INPUTS

DATA I/Os

OPERATION OR FUNCTION

OE

DIR

CLKAB

CLKBA

SAB

SBA

A1–A8

B1–B8

OPERATION OR FUNCTION

X

X

↑

X

X

X

Input

Unspecified†

Store A, B unspecified†

X

XX

↑

X

X

Unspecified†

Input

Store B, A unspecified†

H

X

↑

↑

X

X

Input

Input

Store A and B data

H

X

H or L

H or L

X

X

Input disabled

Input disabled

Isolation, hold storage

L

L

X

X

X

L

Output

Input

Real-time B data to A bus

L

L

X

H or L

X

H

Output

Input

Stored B data to A bus

L

H

X

X

L

X

Input

Output

Real-time A data to B bus

L

H

H or L

X

H

X

Input

Output

Stored A data to B bus

† The data-output functions can be enabled or disabled by various signals at OE and DIR. Data-input functions are always enabled; i.e., data at

the bus terminals is stored on every low-to-high transition of the clock inputs.