4

IDT72255LA/72265LA CMOS SuperSync FIFO™

8,192 x 18 and 16,384 x 18

COMMERCIAL AND INDUSTRIAL

TEMPERATURE RANGES

Symbol

Name

I/O

Description

DataInputs

I

Data inputs for a 18-bit bus.

MRS

MasterReset

I

MRS initializes the read and write pointers to zero and sets the output register to all zeroes. During

Master Reset, the FIFO is configured for either FWFT or IDT Standard mode, one of two program

mableflagdefaultsettings,andserialorparallelprogrammingoftheoffsetsettings.

PRS

PartialReset

I

PRS initializes the read and write pointers to zero and sets the output register to all zeroes. During

Partial Reset, the existing mode (IDT or FWFT), programming method (serial or parallel), and

programmable flag settings are all retained.

RT

Retransmit

I

RT asserted on the rising edge of RCLK initializes the READ pointer to zero, sets the EF flag to

LOW (OR to HIGH in FWFT mode) temporarily and does not disturb the write pointer, programming

method, existing timing mode or programmable flag settings. RT is useful to reread data from the first

physical location of the FIFO.

FWFT/SI

FirstWordFall

I

During Master Reset, selects First Word Fall Through or IDT Standard mode. After Master Reset,

Through/Serial In

thispinfunctionsasaserialinputforloadingoffsetregisters.

WCLK

WriteClock

I

When enabled by WEN, the rising edge of WCLK writes data into the FIFO and offsets into the

programmable registers for parallel programming, and when enabled by SEN, the rising edge of

WCLK writes one bit of data into the programmable register for serial programming.

WEN

Write Enable

I

WEN enables WCLK for writing data into the FIFO memory and offset registers.

RCLK

Read Clock

I

When enabled by REN, the rising edge of RCLK reads data from the FIFO memory and offsets from

theprogrammableregisters.

REN

Read Enable

I

REN enables RCLK for reading data from the FIFO memory and offset registers.

OE

OutputEnable

I

SEN

SerialEnable

I

SENenablesserialloadingofprogrammableflagoffsets.

LD

Load

I

During Master Reset, LD selects one of two partial flag default offsets (127 or 1,023) and determines

the flag offset programming method, serial or parallel. After Master Reset, this pin enables writing to

andreadingfromtheoffsetregisters.

DC

Don't Care

I

FF/IR

Full Flag/

O

In the IDT Standard mode, the FF function is selected. FF indicates whether or not the FIFO

Input Ready

memory is full. In the FWFT mode, the IR function is selected. IR indicates whether or not

there is space available for writing to the FIFO memory.

EF/OR

Empty Flag/

O

In the IDT Standard mode, the EF function is selected. EF indicates whether or not the FIFO

OutputReady

memory is empty. In FWFT mode, the OR function is selected. OR indicates whether or not there is

validdataavailableattheoutputs.

PAF

Programmable

O

PAF goes LOW if the number of words in the FIFO memory is more than total word capacity of the

Almost-FullFlag

FIFO minus the full offset value m, which is stored in the Full Offset register. There are two possible

default values for m: 127 or 1,023.

PAE

Programmable

O

PAE goes LOW if the number of words in the FIFO memory is less than offset n, which is stored in

Almost-EmptyFlag

the Empty Offset register. There are two possible default values for n: 127 or 1,023. Other values

for n can be programmed into the device.

HF

Half-FullFlag

O

HF indicates whether the FIFO memory is more or less than half-full.

DataOutputs

O

Data outputs for an 18-bit bus.

Power

+5 Volt power supply pins.

GND

Ground

Groundpins.

PIN DESCRIPTION