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ST10F271B 数据表(PDF) 40 Page - STMicroelectronics |
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ST10F271B 数据表(HTML) 40 Page - STMicroelectronics |
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40 / 180 page  Internal Flash memory ST10F271B/ST10F271E 40/180 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. 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. 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 / Yes Yes No Fetching from IRAM No / Yes Yes / Yes Yes No Fetching from XRAM No / Yes Yes / Yes Yes No Fetching from External Memory No / Yes Yes / Yes Yes No |
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