CY7C4225-10AXI 데이터 시트보기 (PDF) - Cypress Semiconductor
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CY7C4225-10AXI Datasheet PDF : 25 Pages
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CY7C4205/CY7C4215
CY7C4225/CY7C4245
Flag Operation
The CY7C42X5 devices provide five flag pins to indicate the
condition of the FIFO contents. Empty and Full are synchronous.
PAE and PAF are synchronous if VCC/SMODE is tied to VSS.
Full Flag
The Full Flag (FF) will go LOW when device is Full. Write
operations are inhibited whenever FF is LOW regardless of the
state of WEN. FF is synchronized to WCLK, i.e., it is exclusively
updated by each rising edge of WCLK.
Empty Flag
The Empty Flag (EF) will go LOW when the device is empty.
Read operations are inhibited whenever EF is LOW, regardless
of the state of REN. EF is synchronized to RCLK, i.e., it is
exclusively updated by each rising edge of RCLK.
Programmable Almost Empty/Almost Full Flag
The CY7C42X5 features programmable Almost Empty and
Almost Full Flags. Each flag can be programmed (described in
the Programming section) a specific distance from the
corresponding boundary flags (Empty or Full). When the FIFO
contains the number of words or fewer for which the flags have
been programmed, the PAF or PAE will be asserted, signifying
Table 2. Flag Truth Table
Number of Words in FIFO
CY7C4205 - 256 x 18
CY7C4215 - 512 x 18
0
1 to n[2]
0
1 to n[2]
(n + 1) to 128
(n + 1) to 256
129 to (256 (m + 1))
(256 m)[] to 255
257 to (512 (m + 1))
(512 m)[] to 511
256
512
Number of Words in FIFO
CY7C4225 - 1K x 18
CY7C4245 - 4K x 18
0
1 to n[2]
0
1 to n[2]
(n + 1) to 512
(n + 1) to 2048
513 to (1024 (m + 1))
(1024 m)[3] to 1023
2049 to (4096 (m + 1))
(4096 m)[3] to 4095
1024
4096
that the FIFO is either Almost Full or Almost Empty. See Table 2
for a description of programmable flags.
When the SMODE pin is tied LOW, the PAF flag signal transition
is caused by the rising edge of the write clock and the PAE flag
transition is caused by the rising edge of the read clock.
Retransmit
The retransmit feature is beneficial when transferring packets of
data. It enables the receipt of data to be acknowledged by the
receiver and retransmitted if necessary.
The Retransmit (RT) input is active in the standalone and width
expansion modes. The retransmit feature is intended for use
when a number of writes equal to or less than the depth of the
FIFO have occurred since the last RS cycle. A HIGH pulse on
RT resets the internal read pointer to the first physical location of
the FIFO. WCLK and RCLK may be free running but must be
disabled during and tRTR after the retransmit pulse. With every
valid read cycle after retransmit, previously accessed data is
read and the read pointer is incremented until it is equal to the
write pointer. Flags are governed by the relative locations of the
read and write pointers and are updated during a retransmit
cycle. Data written to the FIFO after activation of RT are
transmitted also.
The full depth of the FIFO can be repeatedly retransmitted.
FF
PAF
HF
PAE
EF
H
H
H
L
L
H
H
H
L
H
H
H
H
H
H
H
H
L
H
H
H
L
L
H
H
L
L
L
H
H
FF
PAF
HF
PAE
EF
H
H
H
L
L
H
H
H
L
H
H
H
H
H
H
H
H
L
H
H
H
L
L
H
H
L
L
L
H
H
Notes
2. n = Empty Offset (Default Values: CY7C4205 n = 31, CY7C4215 n = 63, CY7C4225/CY7C4245 n = 127).
3. m = Full Offset (Default Values: CY7C4205 n = 31, CY7C4215 n = 63, CY7C4225/CY7C4245 n = 127).
Document Number: 001-45652 Rev. *B
Page 7 of 25
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