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IDT72815LB35BG

CMOS DUAL SyncFIFO DUAL 256 x 18, DUAL 512 x 18, DUAL 1024 x 18

Integrated Device Technology 

IDT72805/72815/72825 CMOS Dual SyncFIFO™

256 x 18, 512 x 18, and 1024 x 18

COMMERCIAL TEMPERATURE RANGE

PROGRAMMABLE ALMOST-EMPTY FLAG (PAEA,

PAEB)

The Programmable Almost-Empty Flag (PAEA, PAEB) will

go LOW when the read pointer is “n” locations less than the

write pointer. The offset “n” is defined in the EMPTY offset

register.

If there is no Empty offset specified, PAE will be LOW when

the device is 31 away from completely empty for 72805LB, 63

away from completely empty for 72815LB, and 127 away from

completely empty for 72825LB.

The PAE is asserted LOW on the LOW-to-HIGH transition

of RCLK. PAE is reset to HIGH on the LOW-to-HIGH transition

of WCLK. Thus PAF is asychronous.

WRITE EXPANSION OUT/HALF-FULL FLAG

(WXOA/HFA, WXOB/HFB)

This is a dual-purpose output. In the Single Device and

Width Expansion mode, when WXI is grounded, this output

acts as an indication of a half-full memory.

After half of the memory is filled, and at the LOW-to-HIGH

transition of the next write cycle, the Half-Full Flag goes LOW

and will remain set until the difference between the write

pointer and read pointer is less than or equal to one half of the

total memory of the device. The Half-Full Flag (HFA, HFB) is

then reset to HIGH by the LOW-to-HIGH transition of the read

clock (RCLK). The HF is asychronous.

In the Depth Expansion or Daisy Chain mode, WXI is

connected to WXO of the previous device. This output acts as

a signal to the next device in the Daisy Chain by providing a

pulse when the previous device writes to the last location of

memory.

READ EXPANSION OUT (RXOA, RXOB)

In the Depth Expansion or Daisy Chain configuration, Read

Expansion In (RXIA, RXIB) is connected to Read Expansion

Out (RXOA, RXOB) of the previous device. This output acts as

a signal to the next device in the Daisy Chain by providing a

pulse when the previous device reads from the last location of

memory.

DATA OUTPUTS (Q0A-QA17, QB0-QB17)

Q0-Q17 are data outputs for 18-bit wide data.

RS

REN, WEN, LD

EF , PAE

FF, PAF, HF

Q0 - Q17

t RS

tRSS

t RSF

t RSF

t RSF

t RSR

NOTES:

1. After reset, the outputs will be LOW if OE = 0 and tri-state if OE = 1.

2. The clocks (RCLK, WCLK) can be free-running during reset.

Figure 4. Reset Timing(2)

5.17

OE = 1(1)

OE = 0 3139 drw 04

8

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