S-25C160A Datasheet, PDF (17/39 Pages) Seiko Instruments Inc – Write protect function during the low power supply

Rev.4.2_02_H
SPI SERIAL E²PROM
S-25C160A
5. Write in the status register (WRSR)
The values of status register (SRWD, BP1, BP0) can be rewritten by inputting the WRSR instruction. But b6, b5, b4,
b1, b0 of status register cannot be rewritten. b6 to 4 are always data “0” when reading the status register.
Before inputting the WRSR instruction, set bit WEL by the WREN instruction. The operation of WRSR is shown below.
Set the chip select ( CS ) “L” first. After that, input the instruction code and data from serial data input (SI). To start
WRSR Write (tPR), set the chip select ( CS ) to “H” after inputting data or before inputting a rising of the next serial
clock. It is possible to confirm the operation status by reading the value of bit WIP during WRSR Write. Bit WIP is “1”
during Write, “0” during any other status. Bit WEL is reset when Write is completed.
With the WRSR instruction, the values of BP1 and BP0; which determine the area size the users can handle as the
Read Only memory; can be changed. Besides bit SRWD can be set or reset by the WRSR instruction depending on
the status of Write protect WP . With a combination of bit SRWD and Write protect WP , the device can be set in
Hardware Protect mode (HPM). In this case, the WRSR instruction is not be performed (Refer to “ Protect
Operation”).
Bit SRWD and BP1, BP0 keep the value which is the one prior to the WRSR instruction during the WRSR instruction.
The newly updated value is changed when the WRSR instruction has completed.
To cancel the WRSR instruction, input the clock different from a specified value (n = 16 clocks) while CS is in “L”.
CS
WP
SCK
SI
SO
High / Low
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Instruction
Inputs Data in the Status Register
b7 b6 b5 b4 b3 b2 b1 b0
High-Z
Figure 16 WRSR Operation
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