SN74V215_08 Datasheet, PDF (7/43 Pages) Texas Instruments – 512 X 18, 1024 X 18, 2048 X 18, 4096 X 18 DSP-SYNC FIRST-IN, FIRST-OUT MEMORIES

detailed description (continued)
SN74V215, SN74V225, SN74V235, SN74V245
512 × 18, 1024 × 18, 2048 × 18, 4096 × 18
DSP-SYNC FIRST-IN, FIRST-OUT MEMORIES
SCAS636E – APRIL 2000 – REVISED SEPTEMBER 2002
Table 2. Offset Register Location and Default Values^†
17
12 11
0
Empty Offset Register
Not used
Default Value
003FH (74V215):
007FH (74V225/74V235/74V245)
17
12 11
0
Full Offset Register
Not used
Default Value
003FH (74V215):
007FH (74V225/74V235/74V245)
† _{Any bits of the offset register not being programmed should be set to zero.}
When LD 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 LD is low and REN is low; then, data
can be read on the low-to-high transition of RCLK. Reading the control registers employs a dedicated
read-offset-register pointer. (The read and write pointers operate independently.) Offset register content can be
read out in the standard mode only. It is inhibited in the FWFT mode.
A read from and a write to the offset registers should not be performed simultaneously.
FIRST LOAD (FL)
For the single-device mode, see Table 5 for additional information. In the daisy-chain depth-expansion
configuration, FL is grounded to indicate it is the first device loaded and is set 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. For single-device mode, see Table 5 for additional information. 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. For single-device mode, see Table 5 for additional information. RXI is connected to
read expansion out (RXO) of the previous device in the daisy-chain depth-expansion mode.
OUTPUTS:
FULL FLAG/INPUT READY (FF/IR)
This is a dual-purpose pin. In FWFT mode, the input ready (IR) function is selected. IR goes low when memory
space is available for writing data. When there is no free space left, IR goes high, inhibiting further write
operations.
In standard mode, the FF function is selected. When the FIFO is full, FF goes low, inhibiting further write
operations. When FF is high, the FIFO is not full. If no reads are performed after a reset, FF goes low after
D writes to the FIFO. D = 512 for the SN74V215, 1024 for the SN74V225, 2048 for the SN74V235, and 4096
for the SN74V245.
IR goes high after D writes to the FIFO. D = 513 for the SN74V215, 1025 for the SN74V225, 2049 for the
SN74V235, and 4097 for the SN74V245. The additional word in FWFT mode is due to the capacity of the
memory plus output register.
FF/IR is synchronous and updated on the rising edge of WCLK.
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