Philips Semiconductors

Product specification

74ALS646/74ALS646-1

74ALS648/74ALS648-1

Transceiver/register

1991 Feb 08

5

LOGIC SYMBOL – 74ALS646/646-1

GND = Pin 12

A0

OE

B0

1D

C1

1D

C1

DIR

CPBA

SBA

CPAB

SAB

1 OF 8 CHANNELS

TO 7 OTHER CHANNELS

21

4

20

3

23

22

1

2

SC00124

LOGIC SYMBOL – 74ALS648/648-1

GND = Pin 12

A0

OE

B0

1D

C1

1D

C1

DIR

CPBA

SBA

CPAB

SAB

1 OF 8 CHANNELS

TO 7 OTHER CHANNELS

21

4

20

3

23

22

1

2

SC00125

FUNCTION TABLE

INPUTS

DATA I/O

OPERATING MODE

OE

DIR

CPAB

CPBA

SAB

SBA

An

Bn

74ALS646/74ALS646-1

74ALS648/74ALS648-1

X

X

↑

X

X

X

Input

Unspecified*

Store A, B unspecified*

Store A, B unspecified*

X

X

X

↑

X

X

Unspecified*

Input

Store B, A unspecified*

Store B, A unspecified*

H

X

↑

↑

X

X

Input

Input

Store A and B data

Store A and B data

H

X

H or L

H or L

X

X

Input

Input

Isolation, hold storage

Isolation, hold storage

L

L

X

X

X

L

Output

Input

Real time B data to A bus

Real time B data to A bus

L

L

X

H or L

X

H

Output

Input

Stored B data to A bus

Stored B data to A bus

L

H

X

X

L

X

Input

Output

Real time A data to B bus

Real time A data to B bus

L

H

H or L

X

H

X

Input

Output

Stored A data to B bus

Stored A data to B bus

NOTES:

H = High voltage level

L

= Low voltage level

X = Don’t care

*

= The data output function may be enabled or disabled by various signals at the OE and DIR inputs. Data input functions are always

enabled, i.e., data at the bus pins will be stored on every Low-to-High transition of the clock.

↑ = Low-to-High clock transition