MC68HC908GP20 Datasheet, PDF (180/406 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

11.8 FLASH Block Protection
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.
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 reserving a location in the
memory for block protect information and requiring that this location be
read to enable setting of the HVEN bit. When the block protect register
is read, its contents are latched by the FLASH control logic. If the
address range for an erase or program operation includes a protected
block, the PGM or ERASE bit is cleared which prevents the HVEN bit in
the FLASH control register from being set so that no high voltage is
allowed in the array.
When the block protect register is erased (all 0s), the entire memory is
accessible for program and erase. When bits within the register are
programmed, they lock blocks of memory address ranges as shown in
11.9 FLASH Block Protect Register. The block protect register itself
can be erased or programmed only with an external voltage, V_TST,
present on the IRQ pin. This voltage also allows entry from reset into the
monitor mode.
Advance Information
180
MC68HC908GP20 — Rev 2.1
Freescale Semiconductor