CY7C4255 Datasheet, PDF (16/22 Pages) Cypress Semiconductor – 8K/16K x 18 Deep Sync FIFOs

CY7C4255
CY7C4265
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 stand-alone 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 and at least one word has been
read since the last RS cycle. A HIGH pulse on RT resets the inter-
nal read pointer to the first physical location of the FIFO. WCLK and
RCLK may be free running but must be disabled during and t_RTR
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.
Table 2. Flag Truth Table
Number of Words in FIFO
CY7C4255 – 8K x 18
CY7C4265 – 16K x 18
0
1 to n^[38]
0
1 to n^[38]
(n+1) to 4096
(n+1) to 8192
4097 to (8192–(m+1))
(8192–m)^[39] to 8191
8193 to (16384 –(m+1))
(16384–m)^[39] to 16383
8192
16384
Notes:
38. n = Empty Offset (Default Values: CY7C4255/CY7C4265 n = 127).
39. m = Full Offset (Default Values: CY7C4255/CY7C4265 n = 127).
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
Document #: 38-06004 Rev. *B
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