M25P20 Datasheet, PDF (12/50 Pages) STMicroelectronics – 2 Mbit, Low Voltage, Serial Flash Memory With 25 MHz SPI Bus Interface

Operating features
M25P20
4.5
Status Register
The Status Register contains a number of status and control bits, as shown in Table 6, that
can be read or set (as appropriate) by specific instructions. For a detailed description of the
Status Register bits, see Section 6.4: Read Status Register (RDSR).
4.6
Protection Modes
The environments where non-volatile memory devices are used can be very noisy. No SPI
device can operate correctly in the presence of excessive noise. To help combat this, the
M25P20 features the following data protection mechanisms:
● Power On Reset and an internal timer (t_PUW) can provide protection against inadvertant
changes while the power supply is outside the operating specification.
● Program, Erase and Write Status Register instructions are checked that they consist of
a number of clock pulses that is a multiple of eight, before they are accepted for
execution.
● All instructions that modify data must be preceded by a Write Enable (WREN)
instruction to set the Write Enable Latch (WEL) bit. This bit is returned to its reset state
by the following events:
– Power-up
– Write Disable (WRDI) instruction completion
– Write Status Register (WRSR) instruction completion
– Page Program (PP) instruction completion
– Sector Erase (SE) instruction completion
– Bulk Erase (BE) instruction completion
● The Block Protect (BP1, BP0) bits allow part of the memory to be configured as read-
only. This is the Software Protected Mode (SPM).
● The Write Protect (W) signal, in co-operation with the Status Register Write Disable
(SRWD) bit, allows the Block Protect (BP1, BP0) bits and Status Register Write Disable
(SRWD) bit to be write-protected. This is the Hardware Protected Mode (HPM).
● In addition to the low power consumption feature, the Deep Power-down mode offers
extra software protection from inadvertant Write, Program and Erase instructions, as all
instructions are ignored except one particular instruction (the Release from Deep
Power-down instruction).
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