www.ti.com

DESCRIPTION/ORDERING INFORMATION (CONTINUED)

SN74LVC16646A

16-BIT BUS TRANSCEIVER AND REGISTER

WITH 3-STATE OUTPUTS

SCES408B – AUGUST 2002 – REVISED APRIL 2005

Data on the A or B bus is clocked into the registers on the low-to-high transition of the appropriate clock (CLKAB

or CLKBA) input. Figure 1 illustrates the four fundamental bus-management functions that can be performed with

the SN74LVC16646A.

Output-enable (OE) and direction-control (DIR) inputs control the transceiver functions. In the transceiver mode,

data present at the high-impedance port can be stored in either register or in both. The select-control (SAB and

SBA) inputs can multiplex stored and real-time (transparent mode) data. 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. DIR determines which bus receives data when OE is low. In the isolation mode (OE high), A data

can be stored in one register and/or B data can be stored in the other register.

preventing damaging current backflow through the device when it is powered down.

When an output function is disabled, the input function still is 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.

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.

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

FUNCTION TABLE

INPUTS

OPERATION OR FUNCTION

OE

DIR

CLKAB

CLKBA

SAB

SBA

A1-A8

B1-B8

X

X

↑

X

X

X

Input

Unspecified

X

X

X

↑

X

X

Unspecified

Input

H

X

↑

↑

X

X

Input

Input

Store A and B data

H

X

H or L

H or L

X

X

Input

Input

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 bus

(1)

The data-output functions can be enabled or disabled by various signals at OE or DIR. 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