ST10F272M_12 datasheet(39/176 Pages) STMICROELECTRONICS

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ST10F272M

Internal Flash memory

Doc ID 12968 Rev 3

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When the access protection is enabled, Flash registers can not be written, so no

program/erase operation can be run on IFlash. 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 temporarily 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 temporarily unprotect the Flash when the access protection is active, it is necessary to

set to ‘1’ the bit TAUB in XFVTAUR0. This bit can be set to ‘1’ only while 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.

Note:

The write operation commands must be executed from another memory (internal RAM or

external memory), as in ST10F269 device. In fact, due to IBus characteristics, it is not

possible to perform write operation in Flash while fetching code from Flash.

Moreover, direct addressing is not allowed for write accesses to IFlash control registers.

This means that both address and data for a writing operation must be loaded in one of

ST10 GPR register (R0...R15).

Write operation on IBus registers is 16 bits wide.

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