CAT25C128_05 Datasheet, PDF (8/12 Pages) Catalyst Semiconductor – 128K/256K-Bit SPI Serial CMOS EEPROM

CAT25C128/256
To read the status register, RDSR instruction should be
sent. The contents of the status register are shifted out
on the SO line. The status register may be read at any
time even during a write cycle. Read sequece is illus-
trated in Figure 4. Reading status register is illustrated in
Figure 5.
WRITE Sequence
The CAT25C128/256 powers up in a Write Disable
state. Prior to any write instructions, the WREN instruc-
tion must be sent to CAT25C128/256. The device goes
into Write enable state by pulling the CS low and then
clocking the WREN instruction into CAT25C128/256.
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
Figure 4. Read Instruction Timing
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.
Byte Write
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 25C256 and four most significant bits are don't
care for 25C128), and then the data to be written.
Programming will start after the CS is brought high. Figure
6 illustrates byte write sequence.
During an internal write cycle, all commands will be
ignored except the RDSR (Read Status Register)
instruction.
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
SI
0000001 1
BYTE ADDRESS*
SO
HIGH IMPEDANCE
*Please check the instruction set table for address
Note: Dashed Line= mode (1, 1) — — — —
DATA OUT
7 6 5 432 1 0
MSB
Figure 5. RDSR Timing
CS
SCK
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14
OPCODE
SI
0
0
0
0
0
SO
HIGH IMPEDANCE
Note: Dashed Line= mode (1, 1) — — — —
1
0
1
DATA OUT
7
6
5
4
32
10
MSB
Document No. 1018, Rev. I
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