MAC7200 datasheet(94/976 Pages) FREESCALE

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Security

MAC7200 Microcontroller Family Reference Manual, Rev. 2

Freescale Semiconductor

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Operation from external memory with internal Flash main array and Shadow Block disabled,

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Disabling of EICE and Nexus access in secured Single Chip and Primary Bootloader modes,

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JTAG Test Registers (See Section 35.1.1, “JTAG Test Register (SC4)) are accessible on a secured

device.

Which features are enabled or disabled is determined by the chip mode and security state in effect. Please

refer to Section 2.4.1, “Normal Single Chip Mode to Section 2.4.6, “Secured Expanded Mode for

complete details.

Note that the security state of the Flash is applied to both the Main Array and to the Shadow Block. It is

not possible to unsecure just one or the other.

The user must be reminded that part of the security must lie with the user’s code. An extreme example

would be user’s code that dumps the contents of the internal program. This code would defeat the purpose

of security. At the same time the user may also wish to put a back door in the user’s program. An example

of this is the case in which a user downloads a key through the FlexCAN, allowing access to a

programming routine that updates parameters stored in the Flash.

2.3.1

Operation of the Secured Microcontroller

2.3.1.1

Single Chip Secured Mode

In this mode, the MCU will function similarly to a device in Normal (Unsecured) Single Chip Mode.

However the FlexBus interface will be disabled, and access to the device via the Debug port will be

blocked, thus preventing access to the contents of the memory.

2.3.1.2

Executing from External Memory

The user may wish to execute from external space with a secured microcontroller. This is accomplished

by resetting directly into expanded mode. With the MCU in secure mode, access to the Flash main array

and Shadow Block will be disabled.

2.3.2

Securing the Microcontroller

Once the user has written the contents of the Flash main array and Shadow Block (if desired), the part can

be secured by programming the security bits located in the Shadow Block. These non-volatile bits will

keep the part secured through resetting the part and through powering down the part. When security is

enabled both the Flash main array and Shadow Block memories are secured (i.e.-it is not possible to

configure security independently for these two memories).

For further information on the security of the Flash, consult Section 18.7.9, “Flash Security”.

2.3.3

Unsecuring the Microcontroller

There are two methods to unsecure the MCU:

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Software unsecure

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