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Chapter 4 Memory
MC9S08JS16 MCU Series Reference Manual, Rev. 4
Freescale Semiconductor
47
The value of the checksum bypass is programed by the user. This value is checked by bootloader software
only after power-on reset. The checksum bypass value in this byte indicates if the flash block checksum
will be calculated or not, and if the flash sector whose address is behind the first 1 KB of flash is used as
EEPROM. When the value is other than 0x00 and 0xFF, the calculation of flash block checksum is
bypassed and the code jumps to bootloader entry. When the value is 0xFF, the flash block checksum will
be calculated after power-on reset. When the value is 0x00, the calculation of flash block checksum is
bypassed, the MCU jumps to user code entry and the flash sectors whose addresses are behind the first
1 KB of flash will be used as EEPROM.
The value of this byte is 0xFF when chip is shipped from Freescale.
NOTE
The first 1 KB segment of flash array is not in the CRC checksum
calculation so that users can deploy this area as user EEPROM. If users need
to use other flash locations out of the first 1 KB segment, they need to
re-calculate the CRC and re-program the CRC checksum to ensure reliable
entry after a POR.
4.5.4
Bootloader Operation
This section describes the bootloader mechanism and bootloader flow chart.
The bootloader software is located in bootloader ROM. User can perform flash erasing and programming
when:
•
Bootloader mode is entered
•
Flash block checksum that has been calculated and flash block checksum do not match after
power-on reset
•
SIGNATURE value in register matches
4.5.4.1
Flash Block Checksum
Upon power-on reset (POR), if BLMSS = 0 and the value of checksum bypass is 0xFF, the bootloader will
calculate the flash checksum. The checksum is calculated from the end of first 1 KB of the flash to 0xFFFF
(some bytes in last flash page are skipped). The first 1 KB of flash is not included in the checksum to allow
users to use it as pseudo EEPROM in this area. The calculated checksum are verified with a checksum
written to the two bytes of the flash (FLASHCRC). If the checksum matches, the previous bootloader
operation was successful and the MCU jumps to the user code entry and starts to execute user code. If the
checksum does not match, it jumps to bootloader entry to wait for commands.
Flash block checksum calculation uses 16-bit CRC.
JS16 flash block checksum range is 0xC400–0xFFAD and 0xFFC0–0xFFFF, JS8 flash block checksum
range is 0xE400–0xFFAD and 0xFFC0–0xFFFF.
Содержание HCS08 Series
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Страница 28: ...Chapter 2 Pins and Connections MC9S08JS16 MCU Series Reference Manual Rev 4 28 Freescale Semiconductor...
Страница 34: ...Chapter 3 Modes of Operation MC9S08JS16 MCU Series Reference Manual Rev 4 34 Freescale Semiconductor...
Страница 62: ...Chapter 4 Memory MC9S08JS16 MCU Series Reference Manual Rev 4 62 Freescale Semiconductor...
Страница 114: ...Keyboard Interrupt S08KBIV2 MC9S08JS16 MCU Series Reference Manual Rev 4 114 Freescale Semiconductor...
Страница 146: ...Multi Purpose Clock Generator S08MCGV1 MC9S08JS16 MCU Series Reference Manual Rev 4 146 Freescale Semiconductor...
Страница 166: ...Real Time Counter S08RTCV1 MC9S08JS16 MCU Series Reference Manual Rev 4 166 Freescale Semiconductor...
Страница 186: ...Serial Communications Interface S08SCIV4 MC9S08JS16 MCU Series Reference Manual Rev 4 186 Freescale Semiconductor...
Страница 214: ...16 Bit Serial Peripheral Interface S08SPI16V1 MC9S08JS16 MCU Series Reference Manual Rev 4 214 Freescale Semiconductor...
Страница 274: ...Universal Serial Bus Device Controller S08USBV1 MC9S08JS16 MCU Series Reference Manual Rev 4 274 Freescale Semiconductor...
Страница 282: ...Cyclic Redundancy Check Generator S08CRCV2 MC9S08JS16 MCU Series Reference Manual Rev 4 282 Freescale Semiconductor...
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