mcf51ac256a Freescale Semiconductor, Inc, mcf51ac256a Datasheet - Page 81

• Manufacturer Part Number: mcf51ac256a
• Description: Mcf51ac Flexis
• Manufacturer: Freescale Semiconductor, Inc

Memory
Upon exiting reset, the XCSR[25] bit in the ColdFire CPU is initialized to one if the device is secured, zero
otherwise.
A user can choose to allow or disallow a security unlocking mechanism through an 8-byte backdoor
security key. The security key can be written by the CPU executing from internal memory. It cannot be
entered without the cooperation of a secure user program. The procedure for this is detailed in
Section 4.4.7.1, “Unsecuring the MCU using Backdoor Key Access.”
Development tools will unsecure devices via an alternate BDM-based methodology shown in
Figure
4-15.
Because both RESET and BKGD pins can be reprogrammed via software, a power-on-reset is required to
be absolutely certain of obtaining control of the device via BDM, which is a required prerequisite for
clearing security. Other methods can also be used, but may not work under all circumstances.
MCF51AC256 ColdFire Integrated Microcontroller Reference Manual, Rev. 5
Freescale Semiconductor
4-37