SN74ALVC7804

512

× 18

FIRST-IN, FIRST-OUT MEMORY

SCAS432 – JANUARY 1995

Copyright

1

POST OFFICE BOX 655303

CC

Asynchronous or Coincident

Flag

Load and All Data Outputs Switching

Simultaneously

Package (DL) Using 25-mil Center-to-Center

Spacing

description

A FIFO memory is a storage device that allows

data to be written into and read from its array at

independent data rates. The SN74ALVC7804 is

an 18-bit FIFO with high speed and fast access

times. Data is processed at rates up to 40 MHz

with access times of 18 ns in a bit-parallel format.

The SN74ALVC7804 is designed for 3-V to 3.6-V

Data is written into memory on a low-to-high

transition of the load clock (LDCK) and is read out

on a low-to-high transition of the unload clock

(UNCK). The memory is full when the number of

words clocked in exceeds the number of words clocked out by 512. When the memory is full, LDCK has no effect

on the data residing in memory. When the memory is empty, UNCK has 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 whenever the FIFO contains 256 or more words and is low when it contains 255 or less words. The AF/AE

status flag is a programmable flag. The first one or two low-to-high transitions of LDCK after reset are 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 less words or (512 minus Y) or more words. The AF/AE

flag is low when the FIFO contains between (X plus 1) and (511 minus Y) words.

A low level on the reset (RESET) 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 FIFO must be reset upon power

up. The first word loaded into empty memory causes EMPTY to go high and the data to appear on the Q outputs.

The data outputs are in the high-impedance state when the output-enable (OE) is high.

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.

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RESET

D17

D16

D15

D14

D13

D12

D11

D10

D9

D8

GND

D7

D6

D5

D4

D3

D2

D1

D0

HF

PEN

AF/AE

LDCK

NC

NC

FULL

OE

Q17

Q16

Q15

GND

Q14

Q13

Q12

Q11

Q10

Q9

GND

Q8

Q7

Q6

Q5

Q4

Q3

Q2

GND

Q1

Q0

UNCK

NC

NC

EMPTY

DL PACKAGE

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