SN74ALS990

8-BIT D-TYPE TRANSPARENT READ-BACK LATCH

SDAS027B – APRIL 1984 – REVISED JANUARY 1995

Copyright

1

POST OFFICE BOX 655303

Small-Outline (DW) Packages and Standard

Plastic (N) 300-mil DIPs

description

This 8-bit latch is designed specifically for storing

the contents of the input data bus and providing

the capability of reading back the stored data onto

the input data bus.

The eight latches are transparent D-type latches.

While the latch-enable (LE) input is high, the

Q outputs follow the data (D) inputs.

Read back is provided through the output-enable (OERB) input. When OERB is taken low, the data present at

the output of the data latches is allowed to pass back onto the input data bus. When OERB is taken high, the

output of the data latches is isolated from the D inputs. OERB does not affect the internal operation of the latches;

however, precautions should be taken not to create a bus conflict.

The SN74ALS990 is characterized for operation from 0

°C to 70°C.

C1

11

LE

2D

3

3D

4

4D

5

5D

6

6D

7

7D

8

8D

9

5Q

15

6Q

14

7Q

13

8Q

12

2Q

18

3Q

17

4Q

16

1Q

19

1D

2

1D

EN2

1

OERB

2

† This symbol is in accordance with ANSI/IEEE Std 91-1984 and IEC Publication 617-12.

DW OR N PACKAGE

(TOP VIEW)

1

2

3

4

5

6

7

8

9

10

20

19

18

17

16

15

14

13

12

11

OERB

1D

2D

3D

4D

5D

6D

7D

8D

GND

1Q

2Q

3Q

4Q

5Q

6Q

7Q

8Q

LE

PRODUCTION DATA information is current as of publication date.

Products conform to specifications per the terms of Texas Instruments

standard warranty. Production processing does not necessarily include

testing of all parameters.