Texas Instruments SN74ACT7808-30PM, SN74ACT7808-40FN, SN74ACT7808-40PAG, SN74ACT7808-40PM, SN74ACT7808-20FN Datasheet

SN74ACT7808 2048 ×9 STROBED FIRST-IN, FIRST-OUT MEMORY

SCAS205D ± FEBRUARY 1991 ± REVISED APRIL 1998

DLoad Clocks and Unload Clocks Can Be Asynchronous or Coincident

D2048 Words by 9 Bits

DLow-Power Advanced CMOS Technology

DFast Access Times of 15 ns With a 50-pF Load

DProgrammable Almost-Full/Almost-Empty Flag

description

DExpansion Logic for Depth Cascading

DEmpty, Full, and Half-Full Flags

DFall-Through Time of 20 ns Typical

DData Rates up to 50 MHz

D3-State Outputs

DPackage Options Include 44-Pin Plastic Leaded Chip Carrier (FN), 64-Pin Thin Quad Flat (PM), and Reduced-Height 64-Pin Quad Flat (PAG) Packages

A FIFO memory is a storage device that allows data to be written into and read from its array at independent data rates. The SN74ACT7808 is a 2048-word by 9-bit FIFO designed for high speed and fast access times. It processes data at rates up to 50 MHz and access times of 15 ns in a bit-parallel format.

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 the number of words clocked out by 2048. 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 (FULL), empty (EMPTY), half-full (HF), and almost-full/almost-empty (AF/AE) flags. The FULL output is low when the memory is full and high when the memory is not full. The EMPTY output is low when the memory is empty and high when it is not empty. The HF output is high when the FIFO contains 1024 or more words and is low when it contains 1023 or fewer words. The AF/AE status flag is a programmable flag. The first one or two low-to-high transitions of LDCK after reset can be used to program the almost-empty offset value (X) and the almost-full offset value (Y) if program enable (PEN) is low. The AF/AE flag is high when the FIFO contains X or fewer words or (2048 ± Y) or more words. The AF/AE flag is low when the FIFO contains between (X + 1) and (2047 ± Y) words.

A low level on the reset (RESET) input resets the internal stack pointers and sets FULL high, AF/AE high, HF low, and EMPTY low. The Q outputs are not reset to any specific logic level.

The first word loaded into empty memory 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 in the high-impedance state when the output-enable (OE) input is low. OE does not affect the output flags.

Cascading is easily accomplished in the word-width and word-depth directions. When not using the FIFO in depth expansion, cascade enable (CASEN) must be tied high.

The FIFO must be reset upon power up.

The SN74ACT7808 is characterized for operation from 0°C to 70°C.

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.

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.

Copyright 1998, Texas Instruments Incorporated

POST OFFICE BOX 655303 •DALLAS, TEXAS 75265

1

SN74ACT7808

2048 ×9 STROBED FIRST-IN, FIRST-OUT MEMORY

SCAS205D ± FEBRUARY 1991 ± REVISED APRIL 1998

FN PACKAGE (TOP VIEW)

AF/AE

GND

RESET

GND

V

HF

PEN

V XO

OE

Q0

CC

CC

D0

6

5

4

3

2

1

44 43 42 41 40

Q1

7

39

D1

8

38

VCC

D2

9

37

Q2

GND

10

36

Q3

D3

11

35

GND

D4

12

34

Q4

D5

13

33

VCC

VCC

14

32

Q5

D6

15

31

Q6

D7

30

GND

16

D8

29

Q7

17

18 19 20 21 22 23 24 25 26 27 28

GND

LDCK

DP9

XI

FULL

EMPTY

FL

CASEN

UNCK

Q8

PAG OR PM PACKAGE

Q1 V

Q2

Q3

GND

(TOP VIEW)

Q6

GND

GND

Q7

NC

V

GND

Q4

V

V Q5

CC

CC

CC CC

NC

64 63 62 61 60 59 58

57 56 55 54

53 52 51 50 49

NC

1

48

Q0

Q8

2

47

GND

46

VCC

3

GND

4

45

VCC

OE

5

44

UNCK

XO

CASEN

6

43

VCC

7

42

NC

VCC

8

41

FL

RESET

EMPTY

9

40

PEN

FULL

10

39

GND

XI

11

38

GND

DP9

12

37

AF/AE

LDCK

13

36

HF

GND

14

35

VCC

15

34

GND

VCC

16

33

NC

17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

NC D0

D1

D2

GND

GND

D3

D4

NC

D5 V

V

D6

D7

D8

NC

CC

CC

NC ± No internal connection

2	POST OFFICE BOX 655303 •DALLAS, TEXAS 75265

SN74ACT7808 2048 ×9 STROBED FIRST-IN, FIRST-OUT MEMORY

SCAS205D ± FEBRUARY 1991 ± REVISED APRIL 1998

logic symbol²

F

FIFO 2048 × 9

1

SN74ACT7808

RESET

22

RESET

FULL

FULL

5

19

LDCK

LDCK

HALF FULL

HF

4

26

UNCK

ALMOST FULL/EMPTY

AF/AE

UNCK

23

42

EMPTY

EMPTY

OE

EN1

2

PEN

PROGRAM ENABLE

24

43

FL

FIRST LOAD

EXPANSION OUT

XO

25

CASEN

CASCADE ENABLE

21

XI

EXPANSION IN

20

DATA PIN 9

DP9

7
D0		0				0
8
D1
9
D2
11
D3
12				Data	Data	1
D4
13
D5
15
D6
16
D7
17
D8		8				8

² This symbol is in accordance with ANSI/IEEE Std 91-1984 and IEC Publication 617-12.

Pin numbers shown are for the FN package.

40

Q0

39

Q1

37

Q2

36

Q3

34

Q4

32

Q5

31

Q6

29

Q7

28

Q8

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SN74ACT7808

2048 ×9 STROBED FIRST-IN, FIRST-OUT MEMORY

SCAS205D ± FEBRUARY 1991 ± REVISED APRIL 1998

functional block diagram

	OE
	D0±D8
	UNCK	Read
		Pointer
	LDCK	Write
		Pointer
	DP9
	RESET	Reset
		Logic
		Expansion
	PEN	and
		Status-Flag
	FL	Logic
	CASEN
	XI

Location 1

Location 2

2048 × 9 RAM

Location 2047

Location 2048

Q0±Q8

EMPTY

FULL

HF

AF/AE

XO

4	POST OFFICE BOX 655303 •DALLAS, TEXAS 75265

SN74ACT7808

2048 ×9 STROBED FIRST-IN, FIRST-OUT MEMORY

SCAS205D ± FEBRUARY 1991 ± REVISED APRIL 1998

Terminal Functions

TERMINAL

I/O

DESCRIPTION

NAME

Almost-full/almost-empty flag. Depth-offset values can be programmed for AF/AE or the default value of 256 can be

AF/AE

O

used for both the almost-empty offset (X) and the almost-full offset (Y). AF/AE is high when memory contains X or fewer

words or (2048 ± Y) or more words. AF/AE is high after reset.

Cascade enable. When multiple SN74ACT7808 devices are depth cascaded, every device must have

tied low.

CASEN

CASEN²

I

CASEN must be tied high when a device is not used in depth expansion.

D0±D8

I

Nine-bit data input port

DP9

I

DP9 is used as the most significant bit when programming the AF/AE offset values.

O

Empty flag.

is low when the FIFO memory is empty. A FIFO reset also causes

to go low.

EMPTY

EMPTY

EMPTY

First load. When multiple SN74ACT7808 devices are depth cascaded, the first device in the chain must have its

FL

FL²

I

input tied low and all other devices must have their FL inputs tied high.

O

Full flag.

is low when the FIFO is full. A FIFO reset causes

to go high.

FULL

FULL

FULL

HF

O

Half-full flag. HF is high when the FIFO memory contains 1024 or more words. HF is low after reset.

LDCK

I

Load clock. Data is written to the FIFO on the rising edge of LDCK when

FULL

is high.

OE

I

Output enable. When OE is low, D0±D8 are in the high-impedance state.

Program enable. After reset and before the first word is written to the FIFO, the binary value on D0±D8 and DP9 is

PEN

I

latched as an AF/AE offset value when PEN is low and LDCK is high.

Q0±Q8

O

Nine-bit data output port

I

Reset. A low level on

resets the FIFO and drives

and AF/AE high and HF and

low.

RESET

RESET

FULL

EMPTY

UNCK

I

Unload clock. Data is read from the FIFO on the rising edge of UNCK when

EMPTY

is high.

XI²

I

Expansion input (XI) and expansion output (XO). When multiple SN74ACT7808 devices are depth cascaded, the XO

of one device must be connected to the XI of the next device in the chain. The XO of the last device in the chain is

XO²

O

connected to the XI of the first device in the chain.

² See Figures 6 and 7 for application information on FIFO word-width and word-depth expansions, respectively.

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