HCS08 datasheet(56/374 Pages) NXP

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Chapter 4 Memory

MC9S08JM60 Series Data Sheet, Rev. 5

Freescale Semiconductor

•

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

•

Writing 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

4.5.6

Flash Block Protection

The block protection feature prevents the protected region of flash from program or erase changes. Block

protection is controlled through the flash protection register (FPROT). When enabled, block protection

begins at any 512 byte boundary below the last address of flash, 0xFFFF. (see Section 4.7.4, “Flash

Protection Register (FPROT and NVPROT).”)

After exit from reset, FPROT is loaded with the contents of the NVPROT location which is in the

nonvolatile register block of the flash memory. FPROT cannot be changed directly from application

software so a runaway program cannot alter the block protection settings. Since NVPROT is within the

last 512 bytes of flash, if any amount of memory is protected, NVPROT is itself protected and cannot be

altered (intentionally or unintentionally) by the application software. FPROT can be written through

background debug commands which allows a way to erase and reprogram a protected flash memory.

The block protection mechanism is illustrated below. The FPS bits are used as the upper bits of the last

address of unprotected memory. This address is formed by concatenating FPS7:FPS1 with logic 1 bits as

shown. For example, in order to protect the last 8192 bytes of memory (addresses 0xE000 through

0xFFFF), the FPS bits must be set to 1101 111 which results in the value 0xDFFF as the last address of

unprotected memory. In addition to programming the FPS bits to the appropriate value, FPDIS (bit 0 of

NVPROT) must be programmed to logic 0 to enable block protection. Therefore the value 0xDE must be

programmed into NVPROT to protect addresses 0xE000 through 0xFFFF.

Figure 4-4. Block Protection Mechanism

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

FPS7

FPS6

FPS5

FPS4

FPS3

FPS2

FPS1

A15

A14

A13

A12

A11

A10

A7 A6 A5 A4 A3 A2 A1 A0

111

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