IDT72805LB/72815LB/72825LB/72845LB CMOS Dual SyncFIFOTM
256 x 18, 512 x 18, 1,024 x 18, and 4,096 x 18
COMMERCIAL AND INDUSTRIAL
72815LB/72825LB/72845LB device is functionally equivalent to two
IDT72205LB/72215LB/72225LB/72245LB FIFOs in a single package with all
associated control, data, and flag lines assigned to independent pins. These
devices are very high-speed, low-power First-In, First-Out (FIFO) memories
with clocked read and write controls. These FIFOs are applicable for a wide
Each of the two FIFOs contained in these devices has an 18-bit input and
output port. Each input port is controlled by a free-running clock (WCLK), and
an input enable pin (WEN). Data is read into the synchronous FIFO on every
clock when WEN is asserted. The output port of each FIFO bank is controlled
by another clock pin (RCLK) and another enable pin (REN). The Read Clock
can be tied to the Write Clock for single clock operation or the two clocks can
run asynchronous of one another for dual-clock operation. An Output Enable
pin (OE) is provided on the read port of each FIFO for three-state control of the
The synchronous FIFOs have two fixed flags, Empty Flag/Output Ready
(EF/OR) and Full Flag/Input Ready (FF/IR), and two programmable flags,
Almost-Empty (PAE) and Almost-Full (PAF). The offset loading of the program-
mable flags is controlled by a simple state machine, and is initiated by asserting
the Load pin (LD). A Half-Full flag (HF) is available for each FIFO that is
implemented as a single device configuration.
There are two possible timing modes of operation with these devices: IDT
Standard mode and First Word Fall Through (FWFT) mode.
In IDT Standard Mode, the first word written to an empty FIFO will not
appear on the data output lines unless a specific read operation is performed.
A read operation, which consists of activating REN and enabling a rising RCLK
edge, will shift the word from internal memory to the data output lines.
In FWFT mode, the first word written to an empty FIFO is clocked directly
to the data output lines after three transitions of the RCLK signal. A REN does
not have to be asserted for accessing the first word.
These devices are depth expandable using a daisy-chain technique or First
Word Fall Through (FWFT) mode. The XI and XO pins are used to expand the
FIFOs.Indepthexpansionconfiguration, FL isgroundedonthefirstdeviceand
set to HIGH for all other devices in the Daisy Chain.
The IDT72805LB/72815LB/72825LB/72845LB are fabricated using high-
speed submicron CMOS technology.
WCLKA DA3 DA1
DA0 DB13 DB16 RCLKB LDB
RSB QB17 QB16
B PAFA DA4 WENA DA2 DB12 DB15 RENB OEB EFB QB15 QB14
C FFA RXIA WXIA DA5 DB14 DB11 GND DB17 GND QB13 QB11
D RXOA QA0 QA2 FLA DB8 DB10 DB7 VCC QB12 QB10 QB8
DB6 VCC VCC QB9
QA6 GND VCC GND GND GND VCC GND QB6
QA8 QA10 QA12 VCC DA7 DA10 DA8
FLB QB2 QB0 RXOB
QA11 QA13 GND DA17 GND DA11 DA14 DB5 WXIB RXIB
QA14 QA15 EFA
OEA RENA DA15 DA12 DB2 WENB DB4
QA16 QA17 RSA
LDA RCKLA DA16 DA13 DB0
DB1 DB3 WCLKB
1 2 3 4 5 6 7 8 9 10 11
PBGA (BG121, order code: BG)
1. The PBGA is only available for the IDT72805LB/72815LB/72825LB in the 15 or 25 ns speed grade.
3139 drw 02