Reset

6.5.1Back 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.

NOTE

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).

6.5.2Erase 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.

6.6Reset

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.

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MCF5282 User’s Manual

MOTOROLA

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Motorola MCF5282, MCF5281 user manual Reset, Back Door Access, Erase Verify Check