6
IDT72205LB/72215LB/72225LB/72235LB/72245LB CMOS SyncFIFO
TM
256 x 18, 512 x 18, 1,024 x 18, 2,048 x 18 and 4,096 x 18
COMMERCIAL AND INDUSTRIAL
TEMPERATURE RANGES
MARCH 2013
SIGNAL DESCRIPTIONS:
INPUTS:
DATA IN (D0 - D17)
Data inputs for 18-bit wide data.
CONTROLS:
RESET (RS)
Reset is accomplished whenever the Reset (RS) input is taken to a LOW state.
During reset, both internal read and write pointers are set to the first location.
A reset is required after power-up before a write operation can take place. The
Full Flag (FF), Half-Full Flag (HF) and Programmable Almost-Full Flag (PAF)
will be reset to HIGH after tRSF. The Empty Flag (EF) and Programmable
Almost-Empty Flag (PAE) will be reset to LOW after tRSF. During reset, the output
register is initialized to all zeros and the offset registers are initialized to their default
values.
WRITE CLOCK (WCLK)
A write cycle is initiated on the LOW-to-HIGH transition of the Write Clock
(WCLK). Data setup and hold times must be met with respect to the LOW-to-HIGH
transition of WCLK.
The Write and Read Clocks can be asynchronous or coincident.
WRITE ENABLE (WEN)
When the WEN input is LOW and LD input is HIGH, data may be loaded into
the FIFO RAM array on the rising edge of every WCLK cycle if the device is
not full. Data is stored in the RAM array sequentially and independently of any
ongoing read operation.
When WEN is HIGH, no new data is written in the RAM array on each WCLK
cycle.
To prevent data overflow, FF will go LOW, inhibiting further write operations.
Upon the completion of a valid read cycle, FF will go HIGH allowing a write to
occur. The FF flag is updated on the rising edge of WCLK. WEN is ignored
when the FIFO is full.
READ CLOCK (RCLK)
Data can be read on the outputs on the LOW-to-HIGH transition of the Read
Clock (RCLK), when Output Enable (OE) is set LOW.
The Write and Read Clocks can be asynchronous or coincident.
READ ENABLE (REN)
When Read Enable is LOW and LD input is HIGH, data is loaded from the
RAM array into the output register on the rising edge of every RCLK cycle if
the device is not empty.
When the REN input is HIGH, the output register holds the previous data and
no new data is loaded into the output register. The data outputs Q
0-Qn maintain
the previous data value.
Every word accessed at Qn, including the first word written to an empty
FIFO, must be requested using REN. When the last word has been read from
the FIFO, the Empty Flag (EF) will go LOW, inhibiting further read operations.
REN is ignored when the FIFO is empty. Once a write is performed, EF will
go HIGH allowing a read to occur. The EF flag is updated on the rising edge
of RCLK.
OUTPUT ENABLE (OE)
When Output Enable (OE) is enabled (LOW), the parallel output buffers
receive data from the output register. When OE is disabled (HIGH), the Q output
data bus is in a high-impedance state.
LOAD (LD)
The IDT72205LB/72215LB/72225LB/72235LB/72245LB devices con-
tain two 12-bit offset registers with data on the inputs, or read on the outputs.
When the Load (LD) pin is set LOW and WEN is set LOW, data on the inputs
D0-D11 is written into the Empty Offset register on the first LOW-to-HIGH
transition of the Write Clock (WCLK). When the LD pin and (WEN) are held
LOW then data is written into the Full Offset register on the second LOW-to-HIGH
transition of (WCLK). The third transition of the write clock (WCLK) again writes
to the Empty Offset register.
However, writing all offset registers does not have to occur at one time. One
or two offset registers can be written and then by bringing the LD pin HIGH, the
FIFO is returned to normal read/write operation. When the LD pin is set LOW,
and WEN is LOW, the next offset register in sequence is written.
EMPTY OFFSET REGISTER
17
11
0
001FH (72205) 003FH (72215):
007FH (72225/72235/72245)
FULL OFFSET REGISTER
17
11
0
DEFAULT VALUE
DEFAULT VALUE
001FH (72205) 003FH (72215):
007FH (72225/72235/72245)
2766 drw 05
Figure 2. Write Offset Register
NOTE:
1. The same selection sequence applies to reading from the registers. REN is enabled and
read is performed on the LOW-to-HIGH transition of RCLK.
Figure 3. Offset Register Location and Default Values
NOTE:
1. Any bits of the offset register not being programmed should be set to zero.
LD WEN WCLK Selection
0 0 Writing to offset registers:
Empty Offset
Full Offset
0 1 No Operation
1 0 Write Into FIFO
1 1 No Operation
