Datasheet

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DESCRIPTION/ORDERING INFORMATION (CONTINUED)
SN54LVC652A, SN74LVC652A
OCTAL BUS TRANSCEIVERS AND REGISTERS
WITH 3-STATE OUTPUTS
SCAS303L – JANUARY 1993 – REVISED SEPTEMBER 2005
These devices consist of bus transceiver circuits, D-type flip-flops, and control circuitry arranged for multiplexed
transmission of data directly from the data bus or from the internal storage registers.
Output-enable (OEAB and OEBA) inputs are provided to control the transceiver functions. Select-control (SAB
and SBA) inputs are provided to select whether real-time or stored data is transferred. The circuitry used for
select control eliminates the typical decoding glitch that occurs in a multiplexer during the transition between
stored and real-time data. A low input selects real-time data, and a high input selects stored data. Figure 1
illustrates the four fundamental bus-management functions that are performed with the 'LVC652A devices.
Data on the A or B data bus, or both, is stored in the internal D-type flip-flops by low-to-high transitions at the
appropriate clock (CLKAB or CLKBA) inputs, regardless of the select- or enable-control pins. When SAB and
SBA are in the real-time transfer mode, it is possible to store data without using the internal D-type flip-flops by
simultaneously enabling OEAB and OEBA. In this configuration, each output reinforces its input. When all other
data sources to the two sets of bus lines are at high impedance, each set of bus lines remains at its last state.
Inputs can be driven from either 3.3-V or 5-V devices. This feature allows the use of these devices as translators
in a mixed 3.3-V/5-V system environment.
These devices are fully specified for partial-power-down applications using I
off
. The I
off
circuitry disables the
outputs, preventing damaging current backflow through the device when it is powered down.
To ensure the high-impedance state during power up or power down, OEBA should be tied to V
CC
through a
pullup resistor and OEAB 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.
FUNCTION TABLE
INPUTS DATA I/O
(1)
OPERATION OR FUNCTION
OEAB OEBA CLKAB CLKBA SAB SBA A1–A8 B1–B8
L H H or L H or L X X Input Input Isolation
L H ↑ ↑ X X Input Input Store A and B data
X H ↑ H or L X X Input Unspecified
(2)
Store A, hold B
H H ↑ ↑ X
(2)
X Input Output Store A in both registers
L X H or L ↑ X X Unspecified
(2)
Input Hold A, store B
L L ↑ ↑ X X
(2)
Output Input Store B in both registers
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
H H X X L X Input Output Real-time A data to B bus
H H H or L X H X Input Output Stored A data to B bus
Stored A data to B bus and
H L H or L H or L H H Output Output
stored B data to A bus
(1) The data-output functions can be enabled or disabled by a variety of level combinations at OEAB or OEBA. Data-input functions always
are enabled; i.e., data at the bus terminals is stored on every low-to-high transition of the clock inputs.
(2) Select control = L; clocks can occur simultaneously. Select control = H; clocks must be staggered to load both registers.
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