Datasheet
SCBS700F − JULY 1997 − REVISED AUGUST 2009
2
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
description/ordering information (continued)
Data flow in each direction is controlled by output-enable (OEAB and OEBA), latch-enable (LEAB and LEBA),
and clock (CLKAB and CLKBA) inputs. For A-to-B data flow, the devices operate in the transparent mode when
LEAB is high. When LEAB is low, the A data is latched if CLKAB is held at a high or low logic level. If LEAB is
low, the A data is stored in the latch/flip-flop on the low-to-high transition of CLKAB. When OEAB is high, the
outputs are active. When OEAB is low, the outputs are in the high-impedance state.
Data flow for B to A is similar to that of A to B but uses OEBA
, LEBA, and CLKBA. The output enables are
complementary (OEAB is active high and OEBA
is active low).
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 devices are 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
and OE should be tied to GND through a pulldown resistor; the minimum value of the resistor is determined by
the current-sinking/current-sourcing capability of the driver.
These devices are 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 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.
FUNCTION TABLE
†
INPUTS
OUTPUT
OEAB LEAB CLKAB A
OUTPUT
B
L X X X Z
H HXLL
H HXHH
H L ↑ LL
H L ↑ HH
H LHXB
0
‡
H L L X B
0
§
†
A-to-B data flow is shown; B-to-A flow is similar, but
uses OEBA
, LEBA, and CLKBA.
‡
Output level before the indicated steady-state input
conditions were established, provided that CLKAB
was high before LEAB went low
§
Output level before the indicated steady-state input
conditions were established