Freescale Semiconductor MC68HC908MR32 Manual Do Utilizador
FLASH Memory (FLASH)
MC68HC908MR32 • MC68HC908MR16 Data Sheet, Rev. 6.1
Freescale Semiconductor
43
2.8.5 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 a FLASH block protect register
(FLBPR).
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 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
($FFFF). When the memory is protected, the HVEN bit cannot be set in either ERASE or PROGRAM
operations.
protected area starts from a location defined by FLBPR and ends at the bottom of the FLASH memory
($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
register must be read after setting the PGM or ERASE bit and before
asserting the HVEN bit
register must be read after setting the PGM or ERASE bit and before
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.
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, whose address ranges are
shown in
shown in
. 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 FLBPR itself can be
erased or programmed only with an external voltage, V
erase is disabled whenever any block is protected (FLBPR does not equal $FF). The FLBPR 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.
2.8.6 FLASH Block Protect Register
The FLASH block protect register (FLBPR) is implemented as a byte within the FLASH memory, and
therefore can be written only during a programming sequence of the FLASH memory. The value in this
register determines the starting location of the protected range within the FLASH memory.
therefore can be written only during a programming sequence of the FLASH memory. The value in this
register determines the starting location of the protected range within the FLASH memory.
BPR[7:0] — FLASH Block Protect Bits
These eight bits represent bits [14:7] of a 16-bit memory address. Bit 15 is 1 and bits [6:0] are 0s.
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 and XX80 (128 bytes page boundaries)
within the FLASH memory.
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 and XX80 (128 bytes page boundaries)
within the FLASH memory.
Address:
$FF7E
Bit 7
6
5
4
3
2
1
Bit 0
Read:
BPR7
BPR6
BPR5
BPR4
BPR3
BPR2
BPR1
BPR0
Write:
Reset:
0
0
0
0
0
0
0
0
U = Unaffected by reset. Initial value from factory is 1.
Write to this register by a programming sequence to the FLASH memory.
Write to this register by a programming sequence to the FLASH memory.
Figure 2-5. FLASH Block Protect Register (FLBPR)