CY7C4282
CY7C4292
Document #: 38-06009 Rev. *B
Page 5 of 16
Programmable Almost Empty/Almost Full Flag
The CY7C4282/CY7C4292 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 that the FIFO is either Almost Full or
Almost Empty. See Table 2 for a description of programmable
flags.
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 incriminated 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.
Width-Expansion Configuration
Word width may be increased simply by connecting the corre-
sponding
input
controls
signals
of
multiple
devices.
A composite flag should be created for each of the end-point
status flags (EF and FF). The partial status flags (PAE and
PAF) can be detected from any one device. Figure 2 demon-
strates a 18-bit word width by using two CY7C4282/92. Any
word
width
can
be
attained
by
adding
additional
CY7C4282/92.
When the CY7C4282/92 is in a Width-Expansion Configu-
ration, the Read Enable (REN) control input can be grounded
(see Figure 2). In this configuration, the Load (LD) pin is set to
LOW at Reset so that the pin operates as a control to load and
read the programmable flag offsets.
Notes:
2.
n = Empty Offset (n = 7 default value).
3.
m = Full Offset (m = 7 default value).
Table 2. Status Flags
Number of Words in FIFO
FF
PAF
PAE
EF
CY7C4282
CY7C4292
00
H
H
L
L
1 to n[2]
1 to n[2]
HH
L
H
(n + 1) to (65536
− (m + 1))
(n + 1) to (131072
− (m + 1))
H
H
H
H
(65536
− m)[3] to 65535
(131072
− m)[3] to 131071
H
L
H
H
65536
131072
L
L
H
H
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