M25PE40 Datasheet, PDF (27/62 Pages) STMicroelectronics – 4 Mbit, low voltage, Page-Erasable Serial Flash memory with byte alterability, 50 MHz SPI bus, standard pinout

M25PE40
Instructions
Table 8. Protection modes (T9HX process only, see Important note on page 6)
W SRWD
signal bit
Mode
Write protection of the
Status Register
Memory content
Protected area⁽¹⁾ Unprotected area⁽¹⁾
1
0
Status Register is writable
0
0
Second ^{(if the WREN instruction}
software ^{has set the WEL bit)}
Protected against Ready to accept
Page Program, Page Program and
protected _{The values in the SRWD,} Sector Erase and
Sector Erase
1
1 (SPM2) BP2, BP1 and BP0 bits
Bulk Erase
instructions
can be changed
Status Register is
0
1
Hardware ^{hardware write protected}
protected _{The values in the SRWD,}
(HPM) BP2, BP1 and BP0 bits
Protected against
Page Program,
Sector Erase and
Bulk Erase
Ready to accept
Page Program and
Sector Erase
instructions
cannot be changed
1. As defined by the values in the Block Protect (BP2, BP1, BP0) bits of the Status Register, as shown in
Table 3.
The protection features of the device are summarized in Table 8.
When the Status Register Write Disable (SRWD) bit of the Status Register is 0 (its initial
delivery state), it is possible to write to the Status Register provided that the Write Enable
Latch (WEL) bit has previously been set by a Write Enable (WREN) instruction, regardless
of the whether Write Protect (W) is driven High or Low.
When the Status Register Write Disable (SRWD) bit of the Status Register is set to ‘1’, two
cases need to be considered, depending on the state of Write Protect (W):
● If Write Protect (W) is driven High, it is possible to write to the Status Register provided
that the Write Enable Latch (WEL) bit has previously been set by a Write Enable
(WREN) instruction.
● If Write Protect (W) is driven Low, it is not possible to write to the Status Register even
if the Write Enable Latch (WEL) bit has previously been set by a Write Enable (WREN)
instruction (attempts to write to the Status Register are rejected, and are not accepted
for execution). As a consequence, all the data bytes in the memory area that are
software protected (SPM2) by the Block Protect (BP2, BP1, BP0) bits of the Status
Register, are also hardware protected against data modification.
Regardless of the order of the two events, the Hardware Protected Mode (HPM) can be
entered:
● by setting the Status Register Write Disable (SRWD) bit after driving Write Protect (W)
Low
● or by driving Write Protect (W) Low after setting the Status Register Write Disable
(SRWD) bit.
The only way to exit the Hardware Protected mode (HPM) once entered is to pull Write
Protect (W) High.
If Write Protect (W) is permanently tied High, the Hardware Protected mode (HPM) can
never be activated, and only the Software Protected mode (SPM2), using the Block Protect
(BP2, BP1, BP0) bits of the Status Register, can be used.
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