6

IDT72205LB/72215LB/72225LB/72235LB/72245LB CMOS SyncFIFO™

256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18

Commercial And Industrial Temperature Ranges

LD

WEN

WCLK

Selection

0

0

Writing to offset registers:

Empty Offset

Full Offset

0

1

No Operation

1

0

Write Into FIFO

1

1

No Operation

NOTE:

2766 tbl 08

1. The same selection sequence applies to reading from the registers.

REN

is enabled and read is performed on the LOW-to-HIGH transition of

RCLK.

Figure 2. Write Offset Register

NOTE:

1. Any bits of the offset register not being programmed should be set to zero.

Figure 3. Offset Register Location and Default Values

EMPTY OFFSET REGISTER

17

11

0

001FH (72205) 003FH (72215):

007FH (72225/72235/72245)

FULL OFFSET REGISTER

17

11

0

DEFAULT VALUE

DEFAULT VALUE

001FH (72205) 003FH (72215):

007FH (72225/72235/72245)

2766 drw 05

SIGNAL DESCRIPTIONS:

INPUTS:

Data inputs for 18-bit wide data.

CONTROLS:

RESET (

RS

RS

RS

RS

RS)

Reset is accomplished whenever the Reset (

RS) input is

taken to a LOW state. During reset, both internal read and

write pointers are set to the first location. A reset is required

after power-up before a write operation can take place. The

Full Flag (

FF), Half-Full Flag (HF) and Programmable Almost-

Full Flag (

Flag (

EF) and Programmable Almost-Empty Flag (PAE) will be

initialized to all zeros and the offset registers are initialized to

their default values.

WRITE CLOCK (WCLK)

A write cycle is initiated on the LOW-to-HIGH transition of the

write clock (WCLK). Data set-up and hold times must be met with

respect to the LOW-to-HIGH transition of the write clock (WCLK).

The write and read clocks can be asynchronous or coincident.

WRITE ENABLE (

WEN

WEN

WEN

WEN

WEN)

When the

WEN input is LOW and LD input is HIGH, data

may be loaded into the FIFO RAM array on the rising edge of

every WCLK cycle if the device is not full. Data is stored in the

RAM array sequentially and independently of any ongoing

read operation.

When

WEN is HIGH, no new data is written in the RAM

array on each WCLK cycle.

To prevent data overflow,

FF will go LOW, inhibiting further

write operations. Upon the completion of a valid read cycle,

FF

will go HIGH allowing a write to occur. The

FF flag is updated on

the rising edge of WCLK.

WEN is ignored when the FIFO is full.

READ CLOCK (RCLK)

Data can be read on the outputs on the LOW-to-HIGH transition

of the read clock (RCLK), when Output Enable (

OE) is set LOW.

The write and read clocks can be asynchronous or coincident.

READ ENABLE (

REN

REN

REN

REN

REN)

When Read Enable is LOW and

LD input is HIGH, data is

loaded from the RAM array into the output register on the

rising edge of every RCLK cycle if the device is not empty.

When the

REN input is HIGH, the output register holds the

previous data and no new data is loaded into the output

value.

to an empty FIFO, must be requested using

REN. When the

last word has been read from the FIFO, the Empty Flag (

EF)

will go LOW, inhibiting further read operations.

REN is ignored

when the FIFO is empty. Once a write is performed,

EF will go

HIGH allowing a read to occur. The

EF flag is updated on the

rising edge of RCLK.

OUTPUT ENABLE (

OE

OE

OE

OE

OE)

When Output Enable (

OE) is enabled (LOW), the parallel

output buffers receive data from the output register. When

OE

is disabled (HIGH), the Q output data bus is in a high-

impedance state.

LOAD (

LD

LD

LD

LD

LD)

The IDT72205LB/72215LB/72225LB/72235LB/72245LB

devices contain two 12-bit offset registers with data on the

inputs, or read on the outputs. When the Load (

LD) pin is set

LOW and

WEN is set LOW, data on the inputs D0-D11 is

written into the Empty offset register on the first LOW-to-HIGH

transition of the write clock (WCLK). When the

LD pin and

(

WEN) are held LOW then data is written into the Full offset

register on the second LOW-to-HIGH transition of the write

clock (WCLK). The third transition of the write clock (WCLK)

again writes to the Empty offset register.

However, writing all offset registers does not have to occur

at one time. One or two offset registers can be written and then

by bringing the

LD pin HIGH, the FIFO is returned to normal

read/write operation. When the LD pin is set LOW, and

WEN

is LOW, the next offset register in sequence is written.