ST10F271 datasheet(38/173 Pages) STMICROELECTRONICS

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Internal Flash memory

ST10F271

38/173

When the Access Protection is enabled, Flash registers can not be written, so no

program/erase operation can be run on I-Flash. To enable the access to registers again, the

Temporary Access Unprotection procedure has to be followed (see Section 5.5.9).

5.5.8

Write protection

The Flash modules have one level of Write Protections: each Sector of each Bank of each

Flash Module can be Software Write Protected by programming at 0 the related bit W0Px in

FNVWPIRL register.

5.5.9

Temporary unprotection

Bits W0Px of FNVWPIRL can be temporary unprotected by executing the Set Protection

operation and by writing 1 into these bits.

To restore the write protection bits it is necessary to reset the microcontroller or to execute a

Set Protection operation and write 0 into the desired bits.

In reality, when a temporary write unprotection operation is executed, the corresponding

volatile register is written to 1, while the non volatile registers bits previously written to 0 (for

a protection set operation), will continue to maintain the 0. For this reason, the User

software must be in charge to track the current write protection status (for instance using a

specific RAM area), it is not possible to deduce it by reading the non volatile register content

(a temporary unprotection cannot be detected).

To temporary unprotect the Flash when the Access Protection is active, it is necessary to set

at 1 the bit TAUB in XFVTAUR0. This bit can be write at 1, only executing from Flash: in this

way only an instruction executed from Flash can unprotect the Flash itself.

To restore the Access Protection, it is necessary to reset the microcontroller or to write at 0

the bit TAUB in XFVTAUR0.

5.6

Write operation examples

In the following, examples for each kind of Flash write operation are presented.

Figure 6.

Summary of access protection level

Read IFLASH /

Jump to IFLASH

Read XRAMS or

Ext Mem / Jump to

XRAM or Ext Mem

Read FLASH

Registers

Write FLASH

Registers

Fetching from IFLASH

Yes / Yes

Yes

Fetching from IRAM

No / Yes

Yes / Yes

Yes

Fetching from XRAM

No / Yes

Yes / Yes

Yes

Fetching from External

Memory

No / Yes

Yes / Yes

Yes

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