ST10F272M_12 datasheet(38/176 Pages) STMICROELECTRONICS

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Internal Flash memory

ST10F272M

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Doc ID 12968 Rev 3

5.5.7

Access protection

The IFlash module has one level of access protection (access to data both in reading and

writing).

When bit ACCP of FNVAPR0 is programmed at 0 and bit TAUB in XFVTAUR0 is set at 0, the

IFlash module becomes access protected (data in the IFlash module can be read only if the

current execution is from the IFlash module itself).

Trying to read into the access protected Flash from internal RAM or external memories will

output a dummy data (software trap 009Bh).

When the Flash module is protected in access, data access through PEC transfers is also

forbidden. To read/write data through PEC in a protected bank, first it is necessary to

temporarily unprotect the Flash module.

To enable access protection, the following sequence of operations is recommended:

●

Execution from external memory or internal RAM

●

Program TAUB bit at 1 in XFVTAUR0 register

●

Program ACCP bit in FNVAPR0 to 0 using set protection operation

●

Program TAUB bit at 0 in XFVTAUR0 register

●

Access protection is active when both ACCP bit and TAUB bit are set to 0

Protection can be permanently disabled by programming bit PDS0 of FNVAPR1H, in order

to analyze rejects. Protection can be permanently enabled again by programming bit PEN0

of FNVAPR1L. The action to disable and enable again access protections in a permanent

way can be executed a maximum of 16 times. To execute the above described operations,

the Flash has to be temporarily unprotected (see Section 5.5.9: Temporary unprotection).

Trying to write into the access protected Flash from internal RAM or external memories will

be unsuccessful. Trying to read into the access protected Flash from internal RAM or

external memories will output dummy data (software trap 0x009Bh).

When the Flash module is protected in access, data access through PEC of a peripheral is

also forbidden. To read/write data in PEC mode from/to a protected bank, it is necessary to

first temporarily unprotect the Flash module.

The following table summarizes all possible access protection levels: In particular, it shows

what is possible and not possible to do when fetching from a memory (see fetch location

column) supposing all possible access protections are enabled.

Table 24.

Summary of access protection level

Fetch location

Read IFlash /

jump to IFlash

Read XRAM or

external memory/

jump to XRAM or

external memory

Read Flash

registers

Write Flash

registers

Fetching from IFlash

Yes/yes

Yes

Fetching from IRAM

No/yes

Yes/yes

Fetching from XRAM

No/yes

Yes/yes

Fetching from external

memory

No/yes

Yes/yes

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