AN2153 Freescale Semiconductor / Motorola, AN2153 Datasheet - Page 7

• Manufacturer Part Number: AN2153
• Description: A Serial Bootloader for Reprogramming the MC9S12DP256 FLASH Memory
• Manufacturer: Freescale Semiconductor / Motorola

FLASH Security
AN2153
MOTOROLA
NOTE:
The FLASH protection registers are loaded during the reset sequence
from address $FF0D for FLASH block 0, $FF0C for FLASH block 1,
$FF0B for FLASH block 2 and $FF0A for FLASH block 3. This is
indicated by the “F” in the reset row of the register diagram in the
MC9S12DP256 data book. This register determines whether a whole
block or subsections of a block are protected against accidental program
or erase. Each FLASH block can have two protected areas, one starting
from relative address $8000 (called lower) toward higher addresses and
the other growing downward from $FFFF (called higher). While the later
is mainly targeted to hold the bootloader code since it covers the vector
space (FLASH 0), the other area may be used to keep critical
parameters. Trying to alter any of the protected areas will result in a
protect violation error, and bit PVIOL will be set in the FLASH status
register FSTAT.
A mass or bulk erase of the full 64-Kbyte block is only possible when the
FPLDIS and FPHDIS bits are in the erased state.
The security of a microcontroller’s program and data memories has long
been a concern of companies for one main reason. Because of the
considerable time and money that is invested in the development of
proprietary algorithms and firmware, it is extremely desirable to keep the
firmware and associated data from prying eyes. This was an especially
difficult problem for earlier M68HC12 Family members as the
background debug module (BDM) interface provided easy, uninhibited
access to the FLASH and EEPROM contents using a 2-wire connection.
Later revisions of the original D Family parts provided a method that
Freescale Semiconductor, Inc.
For More Information On This Product,
FPHS[1:0]
0:0
0:1
1:0
1:1
Go to: www.freescale.com
Figure 4. FLASH Protection Select Bits
Protected
16 K
Size
2 K
4 K
8 K
Overview of the MC9S12DP256’s FLASH
FPLS[1:0]
0:0
0:1
1:0
1:1
Protected
512 bytes
Application Note
Size
1 K
2 K
4 K
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