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MC9S08QD4VPC Datasheet(PDF) 43 Page - Freescale Semiconductor, Inc |
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MC9S08QD4VPC Datasheet(HTML) 43 Page - Freescale Semiconductor, Inc |
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43 / 198 page  Chapter 4 Memory Map and Register Definition MC9S08QD4 Series MCU Data Sheet, Rev. 6 Freescale Semiconductor 43 One use for block protection is to block protect an area of flash memory for a bootloader program. This bootloader program then can be used to erase the rest of the flash memory and reprogram it. Because the bootloader is protected, it remains intact even if MCU power is lost in the middle of an erase and reprogram operation. 4.5.7 Vector Redirection Whenever any block protection is enabled, the reset and interrupt vectors will be protected. Vector redirection allows users to modify interrupt vector information without unprotecting bootloader and reset vector space. Vector redirection is enabled by programming the FNORED bit in the NVOPT register located at address 0xFFBF to 0. For redirection to occur, at least some portion but not all of the flash memory must be block protected by programming the NVPROT register located at address 0xFFBD. All of the interrupt vectors (memory locations 0xFFC0–0xFFFD) are redirected, though the reset vector (0xFFFE:FFFF) is not. For example, if 512 bytes of flash are protected, the protected address region is from 0xFE00 through 0xFFFF. The interrupt vectors (0xFFC0–0xFFFD) are redirected to the locations 0xFDC0–0xFDFD. For example, vector redirection is enabled and an interrupt occurs, the values in the locations 0xFDE0:FDE1 are used for the vector instead of the values in the locations 0xFFE0:FFE1. This allows the user to reprogram the unprotected portion of the flash with new program code including new interrupt vector values while leaving the protected area, which includes the default vector locations, unchanged. 4.6 Security The MC9S08QD4 series includes circuitry to prevent unauthorized access to the contents of flash and RAM memory. When security is engaged, flash and RAM are considered secure resources. Direct-page registers, high-page registers, and the background debug controller are considered unsecured resources. Programs executing within secure memory have normal access to any MCU memory locations and resources. Attempts to access a secure memory location with a program executing from an unsecured memory space or through the background debug interface are blocked (writes are ignored and reads return all 0s). Security is engaged or disengaged based on the state of two register bits (SEC01:SEC00) in the FOPT register. During reset, the contents of the nonvolatile location NVOPT are copied from flash into the working FOPT register in high-page register space. A user engages security by programming the NVOPT location, which can be performed at the same time the flash memory is programmed. The 1:0 state disengages security and the other three combinations engage security. Notice the erased state (1:1) makes the MCU secure. During development, whenever the flash is erased, it is good practice to immediately program the SEC00 bit to 0 in NVOPT so SEC01:SEC00 = 1:0. This would allow the MCU to remain unsecured after a subsequent reset. The on-chip debug module cannot be enabled while the MCU is secure. The separate background debug controller can be used for background memory access commands, but the MCU cannot enter active background mode except by holding BKGD/MS low at the rising edge of reset. A user can choose to allow or disallow a security unlocking mechanism through an 8-byte backdoor security key. If the nonvolatile KEYEN bit in NVOPT/FOPT is 0, the backdoor key is disabled and there |
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