CY7C4255
CY7C4265
Document #: 38-06004 Rev. *C
Page 16 of 22
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
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 trans-
mitted also.
The full depth of the FIFO can be repeatedly retransmitted.
Table 2. Flag Truth Table
Number of Words in FIFO
FF
PAF
HF
PAE
EF
CY7C4255 – 8K x 18
CY7C4265 – 16K x 18
00
H
H
H
L
L
1 to n[37]
1 to n[37]
HH
H
L
H
(n + 1) to 4096
(n + 1) to 8192
H
H
H
H
H
4097 to (8192 – (m + 1))
8193 to (16384 – (m + 1))
H
H
L
H
H
(8192 – m)[38] to 8191
(16384 – m)[38] to 16383
H
L
L
H
H
8192
16384
L
L
L
H
H
Notes:
37. n = Empty Offset (Default Values: CY7C4255/CY7C4265 n = 127).
38. m = Full Offset (Default Values: CY7C4255/CY7C4265 n = 127).
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