9

IDT7200/7201A/7202A CMOS ASYNCHRONOUS FIFO

256 x 9, 512 x 9 and 1,024 x 9

MILITARY, INDUSTRIAL AND COMMERCIAL TEMPERATURE RANGES

R

W

HF

2679 drw 11

HALF-FULL OR LESS

MORE THAN HALF-FULL

HALF-FULL OR LESS

Figure 9. Half-Full Flag Timing

R

W

XO

2679 drw 12

WRITE TO

LAST PHYSICAL

LOCATION

READ FROM

LAST PHYSICAL

LOCATION

Figure 10. Expansion Out

W

R

XI

WRITE TO

FIRST PHYSICAL

LOCATION

READ FROM

FIRST PHYSICAL

LOCATION

2679 drw 13

Figure 11. Expansion In

OPERATING MODES:

Care must be taken to assure that the appropriate flag is

monitored by each system (i.e.

FF is monitored on the device

where

W is used; EF is monitored on the device where R is

used). For additional information, refer to Tech Note 8:

Oper-

Tech Note 6:

Designing with FIFOs.

Single Device Mode

A single IDT7200/7201A/7202A may be used when the

application requirements are for 256/512/1,024 words or less.

These devices are in a Single Device Configuration when the

Expansion In (

XI) control input is grounded (see Figure 12).

Depth Expansion

The IDT7200/7201A/7202A can easily be adapted to appli-

cations when the requirements are for greater than 256/512/

1,024 words. Figure 14 demonstrates Depth Expansion using

three IDT7200/7201A/7202As. Any depth can be attained by

adding additional IDT7200/7201A/7202As.

These FIFOs

operate in the Depth Expansion mode when the following

conditions are met:

1. The first device must be designated by grounding the First

Load (

FL) control input.

2. All other devices must have

FL in the high state.

3. The Expansion Out (

XO) pin of each device must be tied

to the Expansion In (

XI) pin of the next device. See Figure

14.

4. External logic is needed to generate a composite Full Flag

(

FF) and Empty Flag (EF). This requires the ORing of all

EFs and ORing of all FFs (i.e. all must be set to generate

the correct composite

FF or EF). See Figure 14.

5. The Retransmit (

RT) function and Half-Full Flag (HF) are

not available in the Depth Expansion Mode.

For additional information, refer to Tech Note 9:

Cascad-

ing FIFOs or FIFO Modules.