Datasheet
SCBS704F − AUGUST 1997 − REVISED OCTOBER 2003
2
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
description/ordering information (continued)
The ’LVTH543 devices contain two sets of D-type latches for temporary storage of data flowing in either
direction. Separate latch-enable (LEAB
or LEBA) and output-enable (OEAB or OEBA) inputs are provided for
each register, to permit independent control in either direction of data flow.
The A-to-B enable (CEAB
) input must be low to enter data from A or to output data from B. If CEAB is low and
LEAB
is low, the A-to-B latches are transparent; a subsequent low-to-high transition of LEAB puts the A latches
in the storage mode. With CEAB
and OEAB both low, the 3-state B outputs are active and reflect the data present
at the output of the A latches. Data flow from B to A is similar, but requires using the CEBA
, LEBA, and OEBA
inputs.
Active bus-hold circuitry holds unused or undriven inputs at a valid logic state. Use of pullup or pulldown resistors
with the bus-hold circuitry is not recommended.
When V
CC
is between 0 and 1.5 V, the device is in the high-impedance state during power up or power down.
However, to ensure the high-impedance state above 1.5 V, OE
should be tied to V
CC
through a pullup resistor;
the minimum value of the resistor is determined by the current-sinking capability of the driver.
This device is fully specified for hot-insertion applications using I
off
and power-up 3-state. The I
off
circuitry
disables the outputs, preventing damaging current backflow through the device when it is 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.
FUNCTION TABLE
†
INPUTS
OUTPUT
CEAB LEAB OEAB A
OUTPUT
B
H X X X Z
X XHXZ
L HLXB
0
‡
L LLLL
L L L H H
†
A-to-B data flow is shown; B-to-A flow control is the
same, except that it uses CEBA
, LEBA, and
OEBA
.
‡
Output level before the indicated steady-state
input conditions were established