SN74AS1821

10BIT BUS INTERFACE FLIPFLOPS WITH 3STATE OUTPUTS

SDAS131 − APRIL 1987

POST OFFICE BOX 655303

Copyright

1

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.

Minimum Lead Inductance in High Current

Switching Applications

Address/Data Paths or Buses with Parity

’AS821 for Plastic and Ceramic Chip Carriers

and “Small Outline” Package Options.

Effects

description

This 10-bit flip-flop device features three-state

outputs designed specifically for driving highly

capacitive or relatively low-impedance loads. It is

particularly suitable for implementing wider buffer

registers, I/O ports, bidirectional bus drivers with

parity, and working registers. The ten flip-flops are

edge-triggered D-type flip-flops. On the positive

transition of the clock, the Q outputs on the

’AS1821 will be true.

A buffered output-control input can be used to

place the ten outputs in either a normal logic state

(high or low levels) or a high-impedance state. In

the high-impedance state the outputs neither load

nor drive the bus lines significantly.

The

high-impedance state and increased drive provide

the capability to drive the bus lines in a

bus-organized system without need for interface

or pull-up components. The output control (OC)

does not affect the internal operation of the

flipflops. Old data can be retained or new data can

be entered while the outputs are in the

high-impedance state.

The SN74AS1821 is characterized for operation

from 0

°C to 70°C.

NT PACKAGE

(TOP VIEW)

FUNCTION TABLE

(each flip-flop)

† This symbol is in accordance with ANSI/IEEE Std 91-1984 and

IEC Publication 617-12.

INPUTS

OUTPUT

LH

X

DQ

CLK

OC

QO

↑

Z

H

L

↑

L

HX

L

LL

X

1

2

3

4

5

6

7

8

9

10

11

12

24

23

22

21

20

19

18

17

16

15

14

13

5Q

4Q

3Q

2Q

1Q

OC

1D

2D

3D

4D

5D

6Q

7Q

8Q

9Q

10Q

CLK

GND

10D

9D

8D

7D

6D

10Q

9Q

8Q

7Q

6Q

5Q

4Q

3Q

2Q

1Q

(20)

(21)

(22)

(23)

(24)

(1)

(2)

(3)

(4)

(5)

10D

9D

8D

7D

6D

5D

4D

3D

2D

1D

CLK

OC

(17)

(16)

(15)

(14)

(13)

(12)

(11)

(10)

(9)

(8)

(19)

(7)

1D

C1

EN