CY7C4255-25AC Cypress Semiconductor Corp, CY7C4255-25AC Datasheet - Page 16

• Manufacturer Part Number: CY7C4255-25AC
• Manufacturer: Cypress Semiconductor Corp

Specifications of CY7C4255-25AC

• Density: 128Kb
• Word Size: 18b
• Sync/async: Synchronous
• Expandable: Yes
• Package Type: TQFP
• Operating Supply Voltage (typ): 5V
• Operating Supply Voltage (min): 4.5V
• Operating Supply Voltage (max): 5.5V
• Operating Temp Range: 0C to 70C
• Operating Temperature Classification: Commercial
• Mounting: Surface Mount
• Pin Count: 64
• Lead Free Status / Rohs Status: Not Compliant

Document #: 38-06004 Rev. *C
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
Table 2. Flag Truth Table
0
1 to n
(n + 1) to 4096
4097 to (8192 – (m + 1))
(8192 – m)
8192
Notes:
37. n = Empty Offset (Default Values: CY7C4255/CY7C4265 n = 127).
38. m = Full Offset (Default Values: CY7C4255/CY7C4265 n = 127).
CY7C4255 – 8K x 18
[37]
[38]
to 8191
Number of Words in FIFO
0
1 to n
(n + 1) to 8192
8193 to (16384 – (m + 1))
(16384 – m)
16384
CY7C4265 – 16K x 18
[37]
[38]
to 16383
internal read pointer to the first physical location of the FIFO.
WCLK and RCLK may be free running but must be disabled
during and t
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.
FF
H
H
H
H
H
L
RTR
after the retransmit pulse. With every valid
PAF
H
H
H
H
L
L
HF
H
H
H
L
L
L
PAE
CY7C4255
CY7C4265
H
H
H
H
L
L
Page 16 of 22
EF
H
H
H
H
H
L
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