CY7C4421/4201/4211/4221
CY7C4231/4241/4251
Document #: 38-06016 Rev. *A
Page 3 of 18
When the device is configured for programmable flags and
both WEN2/LD and WEN1 are LOW, the first LOW-to-HIGH
transition of WCLK writes data from the data inputs to the
empty offset least significant bit (LSB) register. The second,
third, and fourth LOW-to-HIGH transitions of WCLK store data
in the empty offset most significant bit (MSB) register, full offset
LSB register, and full offset MSB register, respectively, when
WEN2/LD and WEN1 are LOW. The fifth LOW-to-HIGH
transition of WCLK while WEN2/LD and WEN1 are LOW
writes data to the empty LSB register again. Figure 1 shows
the registers sizes and default values for the various device
types.
It is not necessary to write to all the offset registers at one time.
A subset of the offset registers can be written; then by bringing
the WEN2/LD input HIGH, the FIFO is returned to normal
Read and Write operation. The next time WEN2/LD is brought
LOW, a Write operation stores data in the next offset register
in sequence.
The contents of the offset registers can be read to the data
outputs when WEN2/LD is LOW and both REN1 and REN2
are LOW. LOW-to-HIGH transitions of RCLK Read register
contents to the data outputs. Writes and reads should not be
preformed simultaneously on the offset registers.
64 × 9
256 × 9512 × 9
8
0
8
0
8
0
8
0
1K × 9
2K × 94K × 98K × 9
(MSB)
0
(MSB)
0
7
1
7
1
8
0
8
0
8
0
8
0
(MSB)
00
(MSB)
00
7
1
7
1
8
0
8
0
8
0
8
0
(MSB)
000
(MSB)
000
7
2
7
2
8
0
8
0
8
0
8
0
Empty Offset (LSB) Reg.
Default Value = 007h
Full Offset (LSB) Reg
Default Value = 007h
(MSB)
0000
(MSB)
0000
7
3
7
3
Empty Offset (LSB) Reg.
Default Value = 007h
Full Offset (LSB) Reg
Default Value = 007h
Empty Offset (LSB) Reg.
Default Value = 007h
Full Offset (LSB) Reg
Default Value = 007h
Empty Offset (LSB) Reg.
Default Value = 007h
Full Offset (LSB) Reg
Default Value = 007h
8
0
8
0
8
0
8
0
Empty Offset (LSB) Reg.
Default Value = 007h
Full Offset (LSB) Reg
Default Value = 007h
(MSB)
00000
(MSB)
00000
7
4
7
4
8
0
8
0
8
0
8
0
65
65
Full Offset (LSB) Reg
Default Value = 007h
Empty Offset (LSB) Reg.
Default Value = 007h
8
0
8
0
8
0
8
0
7
7
Full Offset (LSB) Reg
Default Value = 007h
Empty Offset (LSB) Reg.
Default Value = 007h
Figure 1. Offset Register Location and Default Values
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