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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 Ioff. The Ioff 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 VCC 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.

2