MC908AZ32ACFUE Datasheet, PDF (46/324 Pages) Freescale Semiconductor, Inc – Microcontrollers

Flash Memory
Decreasing the value in FLBPR by one increases the protected range by one page (128 bytes). However,
programming the block protect register with $FE protects a range twice that size, 256 bytes, in the
corresponding array. $FE means that locations $FF00–$FFFF are protected in FLASH.
The FLASH memory does not exist at some locations. The block protection range configuration is
unaffected if FLASH memory does not exist in that range. Refer to the memory map and make sure that
the desired locations are protected.
4.4 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 blocks of memory from unintentional erase or program
operations due to system malfunction. This protection is done by using the FLASH Block Protection
Register (FLBPR). 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 can not be set in either ERASE or
PROGRAM operations.
NOTE
In performing a program or erase operation, the FLASH Block Protect
Register must be read after setting the PGM or ERASE bit and before
asserting the HVEN bit.
When the FLASH Block Protect Register is programmed with all 0’s, the entire memory is protected from
being programmed and erased. When all the bits are erased (all 1’s), the entire memory is accessible for
program and erase.
When bits within FLBPR are programmed (logic 0), they lock a block of memory address ranges as shown
in 4.3.2 FLASH Block Protect Register. If FLBPR is programmed with any value other than $FF, the
protected block of FLASH memory can not be erased or programmed.
NOTE
The vector locations and the FLASH Block Protect Registers are located in
the same page. FLBPR is not protected with special hardware or software;
therefore, if this page is not protected by FLBPR and the vector locations
are erased by either a page or a mass erase operation, FLBPR will also get
erased.
MC68HC908AZ32A Data Sheet, Rev. 2
46
Freescale Semiconductor