M68HC08 datasheet(32/172 Pages) FREESCALE

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Memory

MC68HC908JL3E Family Data Sheet, Rev. 3

Freescale Semiconductor

2.11 FLASH Protection

Due to the ability of the on-board charge pump to erase and program the FLASH memory in the target

application, provision is made to protect blocks of memory from unintentional erase or program operations

due to system malfunction. This protection is done by use of a FLASH Block Protect Register (FLBPR).

The FLBPR determines the range of the FLASH memory which is to be protected. The range of the

protected area starts from a location defined by FLBPR and ends to the bottom of the FLASH memory

($FFFF). When the memory is protected, the HVEN bit cannot be set in either ERASE or PROGRAM

operations.

2.12 FLASH Block Protect Register

The FLASH Block Protect Register is implemented as an 8-bit I/O register. The value in this register

determines the starting address of the protected range within the FLASH memory.

BPR[7:0] — FLASH Block Protect Register Bit 7 to Bit 0

BPR[7:1] represent bits [12:6] of a 16-bit memory address. Bits [15:13] are logic 1’s and bits [5:0] are

logic 0’s.

BPR0 is used only for BPR[7:0] = $FF, for no block protection.

The resultant 16-bit address is used for specifying the start address of the FLASH memory for block

protection. The FLASH is protected from this start address to the end of FLASH memory, at $FFFF.

With this mechanism, the protect start address can be XX00, XX40, XX80, or XXC0 (at page

boundaries — 64 bytes) within the FLASH memory.

Examples of protect start address:

Address:

$FE09

Bit 7

654321

Bit 0

Read:

BPR7

BPR6

BPR5

BPR4

BPR3

BPR2

BPR1

BPR0

Write:

Reset:

00000000

Figure 2-6. FLASH Block Protect Register (FLBPR)

16-bit memory address

Start address of FLASH block protect

1 1 1

000000

BPR[7:1]

BPR[7:0]

Start of Address of Protect Range

$00–$60

The entire FLASH memory is protected.

$62 or $63

(0110 001x)

$EC40 (1110 1100 0100 0000)

$64 or $65

(0110 010x)

$EC80 (1110 1100 1000 0000)

$68 or $69

(0110 100x)

$ED00 (1110 1101 0000 0000)

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