CY7C4801/4811/4821
CY7C4831/4841/4851
256 x 9 x 2
7
512 x 9 x 2
7
1K x 9 x 2
0
0
0
0
8
8
8
8
0
0
0
0
0
0
0
0
8
8
8
8
8
8
8
8
7
Empty Offset (LSB) Reg.
Default Value= 007h
Empty Offset (LSB) Reg.
Default Value = 007h
Empty Offset (LSB) Reg.
Default Value = 007h
1
1
(MSB)
0
(MSB)
00
7
7
7
Full Offset (LSB) Reg
Default Value = 007h
Full Offset (LSB) Reg
Default Value = 007h
Full Offset (LSB) Reg
Default Value = 007h
1
1
(MSB)
0
(MSB)
00
2K x 9 x 2
7
4K x 9 x 2
7
8K x 9 x 2
7
0
0
0
0
0
0
0
0
0
8
8
8
8
8
8
8
8
8
Empty Offset (LSB) Reg.
Default Value = 007h
Empty Offset (LSB) Reg.
Default Value= 007h
Empty Offset (LSB) Reg.
Default Value = 007h
0
0
0
2
8
8
8
3
4
(MSB)
0000
(MSB)
00000
(MSB)
000
7
7
7
Full Offset (LSB) Reg
Default Value = 007h
Full Offset (LSB) Reg
Default Value= 007h
Full Offset (LSB) Reg
Default Value = 007h
2
3
4
(MSB)
000
(MSB)
0000
(MSB)
00000
Figure 1. Offset Register Location and Default Values.
Programmable Flag (PAEA,PAEB, PAFA,PAFB) Operation
The number formed by the empty offset least significant bit
register and empty offset most significant register is referred
to as n and determines the operation of (PAEA,PAEB).
(PAEA,PAEB) is synchronized to the LOW-to-HIGH transition of
RCLK by one flip-flop and is LOW when the FIFO contains n or fewer
unread words. (PAEA,PAEB) is set HIGH by the LOW-to-HIGH tran-
sition of RCLK when the FIFO contains (n+1) or greater unread
words.
Whether the flag offset registers are programmed as de-
scribed in Table 1or the default values are used, the programmable
almost-empty flag (PAEA,PAEB) and programmable almost-full flag
(PAFA,PAFB) states are determined by their corresponding offset
registers and the difference between the read and write pointers.
Table 1. Writing the Offset Registers.
LD WEN WCLK[24]
Selection
The number formed by the full offset least significant bit regis-
ter and full offset most significant bit register is referred to as
m and determines the operation of (PAFA,PAFB). (PAEA,PAEB) is
synchronized to the LOW-to-HIGH transitionof (WCLKA,WCLKB) by
one flip-flop and is set LOW when the number of unread words in the
FIFO is greater than or equal to CY7C4801 (256–m), CY7C4811
(512–m), CY7C4821 (1K–m), CY7C4831 (2K–m), CY7C4841
(4K–m), and CY7C4851 (8K–m). (PAFA,PAFB) is set HIGH by the
LOW-to-HIGH transition of (WCLKA,WCLKB) when the number of
available memory locations is greater than m.
0
0
Empty Offset (LSB)
Empty Offset (MSB)
Full Offset (LSB)
Full Offset (MSB)
0
1
1
0
1
No Operation
Write Into FIFO
No Operation
1
Notes:
24. The same selection sequence applies to reading form the registers. REN1 and REN2 are enabled and a read is performed on the LOW- to-HIGH transition of
RCLK.
Document #: 38-06005 Rev. **
Page 15 of 23
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