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AT32F435/437
Series Reference Manual
2022.11.11
Page 96
Rev 2.03
Each system data occupies two bytes, where the low bytes corresponds to the contents in the system
data area, and the high bytes represent the inverse code that is used to verify the correctness of the
selected bit. When the high byte is not equal to the inverse code of the low byte (except when both high
and low byte are all 0xFF), the system data loader will issue a system data error flag (USDERR) and the
corresponding system data and their inverse codes are forced 0xFF.
Note: The update of the contents in the user system data area becomes effective only after a
system reset.
Table 5-4
User system data area
Address
Bit
Description
0x1FFF_C000
[7: 0]
FAP[7: 0]: Flash memory access protection (Access protection
enable/disable result is stored in the FLASH_USD[1] register )
0xA5: Disabled
Others: Enabled
[15: 8]
nFAP[7: 0]: Inverse code of FAP[7: 0]
[23: 16]
SSB[7:0]: System configuration byte (it is stored in the FLASH_USD[9:
2] register)
Bit 7
Reserved
Bit 6 (nWDT_STDBY)
0: WDT stops counting while entering
Standby mode
1: WDT does not stop counting while
entering Standby mode
Bit 5 (nWDT_DEPSLP)
0: WDT stops counting while entering
Deepsleep mode
1: WDT does not stop counting while
entering Deepsleep mode
Bit 4
Reserved
Bit 3 (BTOPT)
0: When booting from main Flash
memory, if there is no boot loader in the
bank 2, it will starts from bank 1,
otherwise, bank 2.
1: When booting from main Flash
memory, it starts from bank 1.
Bit 2 (nSTDBY_RST)
0: Reset occurs when entering Standby
mode
1: No reset occurs when entering
Standby mode
Bit 1 (nDEPSLP_RST)
0: Reset occurs when entering
Deepsleep mode
1: No reset occurs when entering
Deepsleep mode
Bit 0 (nWDT_ATO_EN)
0: Watchdog is enabled
1: Watchdog is disabled
[31: 24]
nSSB[7: 0]: Inverse code of SSB[7: 0]
0x1FFF_C004
[7: 0]
Data0[7: 0]: User data 0 (It is stored in the FLASH_USD[17:10]
register)
[15: 8]
nData0[7: 0]: Inverse code of Data0[7: 0]
[23: 16]
Data1[7: 0]: User data 1 (It is stored in the FLASH_USD[25: 18]
register)
[31: 24]
nData1[7: 0]: Inverse code of Data1[7: 0]
0x1FFF_C008
[7: 0]
EPP0[7: 0]: Flash erase/write protection byte 0 (in the
FLASH_EPPS[7: 0])
This field is used to protect the 1st~32nd KB of main Flash memory.
Each bit takes care of 4 KB sectors.
0: Erase/write protection is enabled
1: Erase/write protection is disabled
[15: 8]
nEPP0[7: 0]: Inverse code of EPP0[7: 0]
[23: 16]
EPP1[7: 0]: Flash erase/write protection byte 1 (stored in the
FLASH_EPPS[15: 8])
This field is used to protect the 33rd~64th KB of main Flash memory.
Each bit takes care of 4 KB sectors.
0: Erase/write protection is enabled
1: Erase/write protection is disabled
[31: 24]
nEPP1[7: 0]: Inverse code of EPP1[7: 0]
0x1FFF_C00C
[7: 0]
EPP2[7: 0]: Flash erase/write protection byte 2 (stored in the
FLASH_EPPS[23: 16])