Texas Instruments SN74ALS232BDW, SN74ALS232BDWR, SN74ALS232BFN, SN74ALS232BFNR, SN74ALS232BN Datasheet

SN74ALS232B

16 × 4 ASYNCHRONOUS FIRST-IN, FIRST-OUT MEMORY

SCAS251B – FEBRUARY 1989 – REVISED APRIL 1998

1

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

D

Independent Asynchronous Inputs and
Outputs

D

16 Words by 4 Bits

D

Data Rates up to 40 MHz

D

Fall-Through Time 14 ns Typical

D

3-State Outputs

D

Package Options Include Plastic
Small-Outline Package (DW), Plastic Chip
Carriers (FN), and Standard Plastic 300-mil
DIPs (N)

description

This 64-bit memory features high speed and fast
fall-through times. It is organized as 16 words by
4 bits.

A first-in, first-out (FIFO) memory is a storage
device that allows data to be written into and read
from its array at independent data rates. This
FIFO is designed to process data at rates up to
40 MHz in a bit-parallel format, word by word.

Data is written into memory on a low-to-high
transition at the load-clock (LDCK) input and is
read out on a low-to-high transition at the
unload-clock (UNCK) input. The memory is full
when the number of words clocked in exceeds by
16 the number of words clocked out. When the
memory is full, LDCK signals have no effect on the
data residing in memory. When the memory is
empty, UNCK signals have no effect.

Status of the FIFO memory is monitored by the FULL

and EMPTY output flags. The FULL output is low when

the memory is full and high when it is not full. The EMPTY

output is low when the memory is empty and high

when it is not empty.
A low level on the reset (RST

) input resets the internal stack-control pointers and also sets EMPTY low and sets

FULL

high. The Q outputs are not reset to any specific logic level. The first low-to-high transition on LDCK, after

either a RST

pulse or from an empty condition, causes EMPTY to go high and the data to appear on the
Q outputs. It is important to note that the first word does not have to be unloaded. Data outputs are noninverting
with respect to the data inputs and are at high impedance when the output-enable (OE) input is low. OE does
not affect the FULL

or EMPTY output flags. Cascading is easily accomplished in the word-width direction but

is not possible in the word-depth direction.
The SN74ALS232B is characterized for operation from 0°C to 70°C.

Copyright  1998, Texas Instruments Incorporated

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.

OE

FULL

LDCK

D0
D1
D2
D3

GND

DW OR N PACKAGE

(TOP VIEW)

3 2 1 20 19

910111213

4
5
6
7
8

18
17
16
15
14

EMPTY
Q0
NC
Q1
Q2

LDCK

D0

NC

D1
D2

FN PACKAGE

(TOP VIEW)

OE

NC

RST

Q3

UNCK

D3

GND

NC

V

CC

FULL

1
2
3
4
5
6
7
8

16
15
14
13
12
11
10

9

V

CC

UNCK
EMPTY
Q0
Q1
Q2
Q3
RST

NC – No internal connection

Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.

SN74ALS232B
16 × 4 ASYNCHRONOUS FIRST -IN, FIRST-OUT MEMORY

SCAS251B – FEBRUARY 1989 – REVISED APRIL 1998

2

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

logic symbol

†

CT = 0

9

EN4

1

OE

2D

4

D0 Q0

13

5

D1

Q1

12

6

D2

Q2

11

7

D3

Q3

10

15

UNCK

14

(CT = 0) G3

2

(CT = 16) G1

3

LDCK

FIFO 16 × 4

CTR

RST

FULL
EMPTY

3–

1

(+/C2)

4

†

This symbol is in accordance with ANSI/IEEE Standard 91-1984 and IEC Publication 617-12. The symbol is functionally accurate but does
not show the details of implementation; for these, see the logic diagram. The symbol represents the memory as if it were controlled by a single
counter whose content is the number of words stored at the time. Output data is invalid when the counter content (CT) is 0.

Pin numbers shown are for the DW and N packages.

SN74ALS232B

16 × 4 ASYNCHRONOUS FIRST -IN, FIRST-OUT MEMORY

SCAS251B – FEBRUARY 1989 – REVISED APRIL 1998

3

POST OFFICE BOX 655303 • DALLAS, TEXAS 75265

logic diagram (positive logic)

1A, 3D

4

D0

5

D1

6

D2

7

D3

Q0

13

2A

Q1

12

Q2

11

Q3

10

C3

EN

2

14

FULL

EMPTY

RAM 16 × 4

1A

16

2A

16

1

16

1

16

7
8

9
10
11
12
13
14
15
16

1

2

3

4

5

6

+

CT = 1

COMP

P = Q

P= Q+1

P = Q–1

P

Q

1616

S

R

7

8

9
10
11
12
13
14
15
16

1

2

3

4

5

6

+

CT = 1

15

UNCK

C2
2D

S

R

3

LDCK

C1

1D

9

RST

1

OE

Ring

Counter

CTR

DIV 16

Ring

Counter

CTR

DIV 16

Write

Address

Read

Address

16

Pin numbers shown are for the DW and N packages.