25PE20VP datasheet(29/60 Pages) STMICROELECTRONICS

29 / 60 page

M25PE20, M25PE10

Instructions

29/60

The protection features of the device are summarized in Table 10.

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 (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

(BP1, BP0) bits of the Status Register, can be used.

Table 10.

Protection modes (T9HX process only, see Important note on page 6)

Signal

SRWD

Bit

Mode

Write Protection of the

Status Register

Memory Content

Protected Area(1)

As defined by the values in the Block Protect (BP1, BP0) bits of the Status Register, as shown in Table 3.

Unprotected Area(1)

Second

Software

Protected

(SPM2)

Status Register is Writable

(if the WREN instruction

has set the WEL bit)

The values in the SRWD,

BP1 and BP0 bits can be

changed

Protected against

Page Program,

Sector Erase and

Bulk Erase

Ready to accept

Page Program and

Sector Erase

instructions

Hardware

Protected

(HPM)

Status Register is

Hardware write protected

The values in the SRWD,

BP1 and BP0 bits cannot

be changed

Protected against

Page Program,

Sector Erase and

Bulk Erase

Ready to accept

Page Program and

Sector Erase

instructions

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