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Reset
6.5.1
Back Door Access
If the KEYEN bit is set, security can be bypassed by:
1. Setting the KEYACC bit in the CFM configuration register (CFMMCR).
2. Writing the correct 8-byte back door comparison key to the CFM array at addresses
0x0000_0400 to 0x0000_0407. This operation must consist of two 32-bit writes to
address 0x0000_0400 and 0x0000_0404 in that order. The two back door write
cycles can be separated by any number of bus cycles.
3. Clearing the KEYACC bit.
4. If all 8 bytes written match the array contents at addresses 0x0000_0400 to
0x0000_0407, then security is bypassed until the next reset.
The security of the Flash as defined by the Flash security
longword at address 0x0000_0414 is not changed by the back
door method of unsecuring the device. After the next reset the
device is again secured and the same back door key remains in
effect unless changed by program or erase operations. The back
door method of unsecuring the device has no effect on the
program and erase protections defined by the CFM protection
register (CFMPROT).
6.5.2
Erase Verify Check
Security can be disabled by verifying that the CFM array is blank. If required, the mass
erase command can be executed for each pair of Flash physical blocks that comprise the
array. The erase verify command must then be executed for all Flash physical blocks within
the array. The CFM will be unsecured if the erase verify command determines that the
entire array is blank. After the next reset, the security state of the CFM will be determined
by the Flash security longword, which, after being erased, will read 0xffff_ffff, thus
unsecuring the module.
6.6
Reset
The CFM array is not accessible for any operations via the address and data buses during
reset. If a reset occurs while any command is in progress that command will immediately
abort. The state of any longword being programmed or any erase pages/physical blocks
being erased is not guaranteed.
6-24
NOTE
MCF5282 User's Manual
MOTOROLA
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