MC68HC908GR4MP datasheet(114/286 Pages) FREESCALE

114 / 286 page

Flash Memory

MC68HC908GR8 • MC68HC908GR4 Data Sheet, Rev. 7

114

Freescale Semiconductor

11.7 FLASH Block 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 for protecting a block of memory from unintentional erase or program

operations due to system malfunction. This protection is done by using 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 at the bottom of the FLASH

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

PROGRAM operations.

NOTE

In performing a program or erase operation, the FLASH block protect

asserting the HVEN bit

When the FLBPR is programmed with all 0s, the entire memory is protected from being programmed and

erased. When all the bits are erased (all 1s), the entire memory is accessible for program and erase.

When bits within the FLBPR are programmed, they lock a block of memory with address ranges as shown

in FLASH Block Protect Register. Once the FLBPR is programmed with a value other than $FF, any erase

or program of the FLBPR or the protected block of FLASH memory is prohibited. Mass erase is disabled

whenever any block is protected (FLBPR does not equal $FF). The presence of a VTST on the IRQ pin

will bypass the block protection so that all of the memory included in the block protect register is open for

program and erase operation.

NOTE

The FLASH block protect register is not protected with special hardware or

software. Therefore, if this page is not protected by FLBPR, the register is

erased by either a page or mass erase operation.

11.7.1 FLASH Block Protect Register

The FLASH block protect register (FLBPR) is implemented as a byte within the FLASH memory, and

therefore can only be written during a programming sequence of the FLASH memory. The value in this

BPR[7:0] — FLASH Block Protect Bits

These eight bits represent bits [13:6] of a 16-bit memory address. Bits [15:14] are 1s and bits [5:0]

are 0s.

Address:

$FF7E

Bit 7

654321

Bit 0

Read:

BPR7

BPR6

BPR5

BPR4

BPR3

BPR2

BPR1

BPR0

Write:

Reset:

UUUUUUUU

U = Unaffected by reset. Initial value from factory is 1.

Write to this register is by a programming sequence to the FLASH memory.

Figure 11-3. FLASH Block Protect Register (FLBPR)

MC68HC908GR4MP Datasheet(PDF) 114 Page - Freescale Semiconductor, Inc

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