COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
IDT723631/723641/723651 CMOS SyncFIFO™
512 x 36, 1,024 x 36 and 2,048 x 36
3
PIN DESCRIPTION
Symbol Name I/O Description
A0-A35 Port-A Data I/O 36-bit bidirectional data port for side A.
AE Almost-Empty O Programmable flag synchronized to CLKB. It is LOW when the number of words in the FIFO is less than or equal to the value in
Flag the Almost-Empty register (X).
AF Almost-Full O Programmable flag synchronized to CLKA. It is LOW when the number of empty locations in FIFO is less than or equal to the
Flag value in the Almost-Full Offset register (Y).
B0-B35 Port-B Data I/O 36-bit bidirectional data port for side B.
CLKA Port-A Clock I CLKA is a continuous clock that synchronizes all data transfers through port-A and may be asynchronous or coincident to CLKB.
IR and AF are synchronous to the LOW-to-HIGH transition of CLKA.
CLKB Port-B Clock I CLKB is a continuous clock that synchronizes all data transfers through port-B and may be asynchronous or coincident to CLKA.
OR and AE are synchronous to the LOW-to-HIGH transition of CLKB.
CSA Port-A Chip I CSA must be LOW to enable a LOW-to-HIGH transition of CLKA to read or write data on port-A. The A0-A35 outputs are in the
Select high-impedance state when CSA is HIGH.
CSB Port-B Chip I CSB must be LOW to enable a LOW-to-HIGH transition of CLKB to read or write data on port-B. The B0-B35 outputs are in the
Select high-impedance state when CSB is HIGH.
EN A Port-A Enable I ENA must be HIGH to enable a LOW-to-HIGH transition of CLKA to read or write data on port-A.
EN B Port-B Enable I ENB must be HIGH to enable a LOW-to-HIGH transition of CLKB to read or write data on port-B.
FS1/ Flag-Offset I FS1/SEN and FS0/SD are dual-purpose inputs used for flag Offset register programming. During a device reset, FS1/SEN and
SEN, Select 1/ FS0/SD selects the flag offset programming method. Three Offset register programming methods are available: automatically
Serial Enable load one of two preset values, parallel load from port A, and serial load.
FS0/SD Flag Offset 0/ When serial load is selected for flag Offset register programming, FS1/SEN is used as an enable synchronous to the LOW-to-
Serial Data HIGH transition of CLKA. When FS1/SEN is LOW, a rising edge on CLKA load the bit present on FS0/SD into the X and Y
registers. The number of bit writes required to program the Offset registers is 18/20/22. The first bit write stores the Y-register
MSB and the last bit write stores the X-register LSB.
IR Input Ready O IR is synchronized to the LOW-to-HIGH transition of CLKA. When IR is LOW, the FIFO is full and writes to its array are
Flag disabled. When the FIFO is in retransmit mode, IR indicates when the memory has been filled to the point of the retransmit
data and prevents further writes. IR is set LOW during reset and is set HIGH after reset.
MBA Port-A Mailbox I A HIGH level chooses a mailbox register for a port-A read or write operation.
Select
MBB Port-B Mailbox I A HIGH level chooses a mailbox register for a port-B read or write operation. When the B0-B35 outputs are active, a HIGH
Select level on MBB selects data from the mail1 register for output and a LOW level selects FIFO data for output.
MBF1 Mail1 Register O MBF1 is set LOW by the LOW-to-HIGH transition of CLKA that writes data to the mail1 register. MBF1 is set HIGH by a
Flag LOW-to-HIGH transition of CLKB when a port-B readis selected and MBB is HIGH. MBF1 is set HIGH by a reset.
MBF2 Mail2 Register O MBF2 is set LOW by the LOW-to-HIGH transition of CLKB that writes data to the mail2 register. MBF2 is set HIGH by a
Flag LOW-to-HIGH transition of CLKA when a port-A read is selected and MBA is HIGH. MBF2 is set HIGH by a reset.
OR Output Ready O OR is synchronized to the LOW-to-HIGH transition of CLKB. When OR is LOW, the FIFO is empty and reads are disabled.
Flag Ready data is present in the output register of the FIFO when OR is HIGH. OR is forced LOW during the reset and goes
HIGH on the third LOW-to-HIGH transition of CLKB after a word is loaded to empty memory.
RFM Read From I When the FIFO is in retransmit mode, a HIGH on RFM enables a LOW-to-HIGH transition of CLKB to reset the read pointer
Mark to the beginning retransmit location and output the first selected retransmit data.
RST Reset I To reset the device, four LOW-to-HIGH transitions of CLKA and four LOW-to-HIGH transitions of CLKB must occur while RST
is LOW. The LOW-to-HIGH transition of RST latches the status of FS0 and FS1 for AF and AE offset selection.
RTM Retransmit I When RTM is HIGH and valid data is present in the FIFO output register (OR is HIGH), a LOW-to-HIGH transition of CLKB
Mode selects the data for the beginning of a retransmit and puts the FIFO in retransmit mode. The selected word remains the initial
retransmit point until a LOW- to-HIGH transition of CLKB occurs while RTM is LOW, taking the FIFO out of retransmit mode.
W/RA Port-A Write/ I A HIGH selects a write operation and a LOW selects a read operation on port A for a LOW-to-HIGH transition of CLKA. The
Read Select A0-A35 outputs are in the high-impedance state when W/RA is HIGH.
W/RB Port-B Write/ I A LOW selects a write operation and a HIGH selects a read operation on port B for a LOW-to-HIGH transition of CLKB. The
Read Select B0-B35 outputs are in the high-impedance state when W/RB is LOW.
