MC68HC908MR8 Datasheet, PDF (62/372 Pages) Motorola, Inc – Microcontrollers

FLASH Memory
4.3.1 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 a FLASH protection
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 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 block protect register is erased (all 1s), the entire memory is
accessible for program and erase. When bits within the register are
programmed (set to 0), they lock blocks of memory address ranges as
shown in 4.3.2 FLASH Block Protect Register. Once the block protect
register is programmed with value other than $FF, any erase or program
of the block protect register or the protected pages will be prohibited. The
block protect register itself can be erased or programmed only with an
external voltage V_HI present on the IRQ pin. The presence of V_HI on the
IRQ pin also allows entry into monitor mode out of reset. Therefore, the
ability to change the block protect register is voltage dependent and can
occur in either user or monitor modes.
Technical Data
62
FLASH Memory
MC68HC908MR8 — Rev 4.1
Freescale Semiconductor