st10f272z2 STMicroelectronics, st10f272z2 Datasheet - Page 40

• Manufacturer Part Number: st10f272z2
• Description: 16-bit Mcu With 256 Kbyte Flash Memory And 20 Kbyte Ram
• Manufacturer: STMicroelectronics

Internal Flash memory
5.5.8
5.5.9
40/189
way can be executed a maximum of 16 times. To execute the above described operations,
the Flash has to be temporary unprotected (See
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 a dummy data (software trap 0x009Bh).
When the Flash module is protected in access, also the data access through PEC of a
peripheral is forbidden. To read/write data in PEC mode from/to a protected Bank, first it is
necessary to temporary unprotect the Flash module.
In the following table a summary of all levels of possible Access protection is reported: in
particular, supposing to enable all possible access protections, when fetching from a
memory as listed in the first column, what is possible and what is not possible to do (see
column headers) is shown in the table.
Figure 6.
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
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.
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.
Fetching from IFLASH
Fetching from IRAM
Fetching from XRAM
Fetching from External
Memory
Summary of access protection level
Jump to IFLASH
Read IFLASH /
Yes / Yes
No / Yes
No / Yes
No / Yes
Ext Mem / Jump to
XRAM or Ext Mem
Read XRAMS or
Yes / Yes
Yes / Yes
Yes / Yes
Yes / Yes
Section 5.5.9: Temporary
Read FLASH
Registers
Yes
Yes
Yes
Yes
Section
unprotection)
5.5.9).
Write FLASH
ST10F272Z2
Registers
No
No
No
No