IDT72205LB/72215LB/72225LB/72235LB/72245LB CMOS SyncFIFO™
256 x 18-BIT, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18
Commercial And Industrial Temperature Ranges
When the
LD
pin is LOW and
WEN
is HIGH, the WCLK input
is disabled; then a signal at this input can neither increment the
write offset register pointer, nor execute a write.
The contents of the offset registers can be read on the
output lines when the
LD
pin is set LOW and
REN
is set LOW;
then, data can be read on the LOW-to-HIGH transition of the
read clock (RCLK). The act of reading the control registers
employs a dedicated read offset register pointer. (The read
and write pointers operate independently).
A read and a write should not be performed simultaneously
to the offset registers.
FIRST LOAD (
FL
)
FL
is grounded to indicate operation in the Single Device or
Width Expansion mode. In the Depth Expansion configuration,
FL
is grounded to indicate it is the first device loaded and is set
to HIGH for all other devices in the Daisy Chain. (See Operating
Configurations for further details.)
WRITE EXPANSION INPUT (
WXI
)
This is a dual purpose pin.
WXI
is grounded to indicate
operation in the Single Device or Width Expansion mode.
WXI
is connected to Write Expansion Out (
WXO
) of the previous
device in the Daisy Chain Depth Expansion mode.
READ EXPANSION INPUT (
RXI
)
This is a dual purpose pin.
RXI
is grounded to indicate
operation in the Single Device or Width Expansion mode.
RXI
is connected to Read Expansion Out (
RXO
) of the previous
device in the Daisy Chain Depth Expansion mode.
EMPTY FLAG (
EF
)
When the FIFO is empty,
EF
will go LOW, inhibiting further
read operations. When
EF
is HIGH, the FIFO is not empty.
The EF is updated on the LOW-to-HIGH transition of the
read clock (RCLK).
PROGRAMMABLE ALMOST-FULL FLAG (
PAF
)
The Programmable Almost-Full Flag (
PAF
) will go LOW
when FIFO reaches the Almost-Full condition. If no reads are
performed after Reset (
RS
), the
PAF
will go LOW after (256-m)
writes for the IDT72205LB, (512-m) writes for the IDT72215LB,
(1,024-m) writes for the IDT72225LB, (2,048–m) writes for the
IDT72235LB and (4,096–m) writes for the IDT72245LB. The
offset “m” is defined in the FULL offset register.
If there is no Full offset specified, the
PAF
will be LOW when
the device is 31 away from completely full for IDT72205LB, 63
away from completely full for IDT72215LB, and 127 away from
completely full for IDT72225LB/72235LB/72245LB.
The
PAF
is asserted LOW on the LOW-to-HIGH transition
of the write clock (WCLK).
PAF
is reset to HIGH on the LOW-
to-HIGH transition of the read clock (RCLK). Thus
PAF
is
asynchronous.
PROGRAMMABLE ALMOST-EMPTY FLAG (
PAE
)
The Programmable Almost-Empty Flag (
PAE
) will go LOW
when the read pointer is “n+1” locations less than the write
pointer. The offset “n” is defined in the EMPTY offset register.
If there is no Empty offset specified, the Programmable
Almost-Empty Flag (
PAE
) will be LOW when the device is 31
away from completely empty for IDT72205LB, 63 away from
completely empty for IDT72215LB, and 127 away from com-
pletely empty for IDT72225LB/72235LB/72245LB.
The
PAE
is asserted LOW on the LOW-to-HIGH transition
of the read clock (RCLK).
PAE
is reset to HIGH on the LOW-
to-HIGH transition of the write clock (WCLK). Thus
PAE
is
asynchronous.
WRITE EXPANSION OUT/HALF-FULL FLAG (
WXO
/
HF
)
This is a dual-purpose output. In the Single Device and
Width Expansion mode, when Write Expansion In (
WXI
) and
Read Expansion In (
RXI
) are grounded, this output acts as an
indication of a half-full memory.
OUTPUTS:
FULL FLAG (
FF
)
When the FIFO is full,
FF
will go LOW, inhibiting further
write operations. When
FF
is HIGH, the FIFO is not full. If no
reads are performed after a reset,
FF
will go LOW after D
writes to the FIFO. D = 256 writes for the IDT72205LB, 512 for
the IDT72215LB, 1,024 for the IDT72225LB, 2,048 for the
IDT72235LB and 4,096 for the IDT72245LB.
The
FF
is updated on the LOW-to-HIGH transition of the
write clock (WCLK).
TABLE I — STATUS FLAGS
72205
0
1 to n
(1)
(n + 1) to 128
(256-m)
(2)
72215
0
1 to n
(1)
Number of Words in FIFO Memory
72225
72235
0
1 to n
(1)
(n + 1) to 512
(1,024-m)
(2)
to 1,023
0
1 to n
(1)
(n + 1) to 1,024
(2,048-m)
(2)
to 2,047
72245
0
1 to n
(1)
(n + 1) to 2,048
(4,096-m)
(2)
to 4,095
FF PAF HF PAE EF
H
H
H
H
H
L
H
H
H
H
L
L
H
H
H
L
L
L
L
L
H
H
H
H
L
H
H
H
H
H
(n + 1) to 256
(512-m)
(2)
512
to 511
129 to (256-(m+1)) 257 to (512-(m+1)) 513 to (1,024-(m+1)) 1,025 to (2,048-(m+1)) 2,049 to (4,096-(m+1))
to 255
256
1,024
2,048
4,096
NOTES:
1. n = Empty Offset (Default Values : IDT72205 n=31, IDT72215 n = 63, IDT72225/72235/72245 n = 127)
2. m = Full Offset (Default Values : IDT72205 n=31, IDT72215 n = 63, IDT72225/72235/72245 n = 127)
2766 tbl 09
7
IDT [ INTEGRATED DEVICE TECHNOLOGY ]
