MC9S08GB60A Datasheet, PDF (55/302 Pages) Freescale Semiconductor, Inc – HCS08 Microcontrollers

Chapter 4 Memory
4.4.5 Access Errors
An access error occurs whenever the command execution protocol is violated.
Any of the following specific actions will cause the access error flag (FACCERR) in FSTAT to be set.
FACCERR must be cleared by writing a 1 to FACCERR in FSTAT before any command can be processed.
• Writing to a flash address before the internal flash clock frequency has been set by writing to the
FCDIV register
• Writing to a flash address while FCBEF is not set (A new command cannot be started until the
command buffer is empty.)
• Writing a second time to a flash address before launching the previous command (There is only
one write to flash for every command.)
• Writing a second time to FCMD before launching the previous command (There is only one write
to FCMD for every command.)
• Writing to any flash control register other than FCMD after writing to a flash address
• Writing any command code other than the five allowed codes (0x05, 0x20, 0x25, 0x40, or 0x41)
to FCMD
• Accessing (read or write) any flash control register other than the write to FSTAT (to clear FCBEF
and launch the command) after writing the command to FCMD
• The MCU enters stop mode while a program or erase command is in progress (The command is
aborted.)
• Writing the byte program, burst program, or page erase command code (0x20, 0x25, or 0x40) with
a background debug command while the MCU is secured (The background debug controller can
only do blank check and mass erase commands when the MCU is secure.)
• Writing 0 to FCBEF to cancel a partial command
4.4.6 Flash Block Protection
Block protection prevents program or erase changes for flash memory locations in a designated address
range. Mass erase is disabled when any block of flash is protected. The MC9S08GBxxA/GTxxA allows a
block of memory at the end of flash, and/or the entire flash memory to be block protected. A disable control
bit and a 3-bit control field, allows the user to set the size of this block. A separate control bit allows block
protection of the entire flash memory array. All seven of these control bits are located in the FPROT
register (see Section 4.6.4, “Flash Protection Register (FPROT and NVPROT)”).
At reset, the high-page register (FPROT) is loaded with the contents of the NVPROT location which is in
the nonvolatile register block of the flash memory. The value in FPROT cannot be changed directly from
application software so a runaway program cannot alter the block protection settings. If the last 512 bytes
of flash which includes the NVPROT register is protected, the application program cannot alter the block
protection settings (intentionally or unintentionally). The FPROT control bits can be written by
background debug commands to allow a way to erase a protected flash memory.
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.
MC9S08GB60A Data Sheet, Rev. 2
Freescale Semiconductor
55