CAT25C32/64
Advanced Information
WRITE Sequence
Byte Write
The CAT25C32/64 powers up in a Write Disable state.
Prior to any write instructions, the WREN instruction
must be sent to CAT25C32/64. The device goes into
Write enable state by pulling the CS low and then
clocking the WREN instruction into CAT25C32/64. The
CS must be brought high after the WREN instruction to
enable writes to the device. If the write operation is
initiated immediately after the WREN instruction without
CS being brought high, the data will not be written to the
array because the write enable latch will not have been
properly set. Also, for a successful write operation the
address of the memory location(s) to be programmed
must be outside the protected address field location
selected by the block protection level.
Once the device is in a Write Enable state, the user may
proceed with a write sequence by setting the CS low,
issuing a write instruction via the SI line, followed by the
16-bit address (the three Most Significant Bits are don’t
care for 25C64 and four most significant bits are don't
care for 25C32), and then the data to be written. Pro-
gramming will start after the CS is brought high. Figure
6 illustrates byte write sequence.
Figure 4. Read Instruction Timing
CS
0
1
2
3
4
5
6
7
8
9
10
20 21 22 23 24 25 26 27 28 29 30
SK
OPCODE
BYTE ADDRESS*
SI
0
0
0
0
0
0
1
1
DATA OUT
HIGH IMPEDANCE
SO
7
6
5
4
3
2
1
0
MSB
*Please check the instruction set table for address
Note: Dashed Line= mode (1, 1) — — — —
Figure 5. RDSR Instruction Timing
CS
0
1
2
3
4
5
1
6
0
7
1
8
9
10
11
12
13
14
SCK
OPCODE
0
0
0
0
0
SI
DATA OUT
HIGH IMPEDANCE
SO
5
7
6
4
3
2
1
0
MSB
Note: Dashed Line= mode (1, 1) — — — —
Doc No. 25087 -00 8/99 SPI-1
7
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