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MCU Mode Selection

MAC7200 Microcontroller Family Reference Manual, Rev. 2

Freescale Semiconductor

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JTAG Lockout Recovery

2.3.3.1

Software Unsecure

Since the security state of the device is determined solely by a user programmable location in the Shadow

Block, any application may choose to implement a software unsecure method, through any interface.

There are no built-in features, such as a backdoor access key, on the MAC72xx.

2.3.3.2

JTAG Lockout Recovery

If a software unsecure of the device is not possible, an alternative method exists for unsecuring the device.

In this method, called Lockout Recovery, the Flash main array and Shadow Block are first erased before

the device is unsecured. This procedure can be performed with a JTAG instruction over the JTAG interface

of the device. The recommended procedure is as follows:

1. Assert the RESET to the device

2. While the RESET is asserted, set the “Start Flash Lockout Recovery” bit (bit 9) in JTAG Test

3. Release the RESET

4. The JTAG Lockout Recovery procedure will run automatically, erasing both the Flash main array

and the Shadow Block, followed by a re-programming of the security bits to an unsecured state.

5. Sample the JTAG Test Register SC4 until the “Flash Lockout Recovery is complete” bit (bit 8) is

set

6. If the “Flash Security Request” bit (bit 19) is cleared, the device is now unsecured

7. Reset the device again in order to leave JTAG Lockout Recovery mode. There is no need to clear

the “Start Flash Lockout Recovery” or “Flash Lockout Recovery is complete” bits, as they are

self-clearing.

Note that performing Lockout Recovery erases both the Flash main array and the Shadow Block.

2.4

MCU Mode Selection

The chip operating mode out of Reset is determined by the states of the MODA and MODB pins (Port

D[1:0]) at Reset and the security status of the Program Flash.

Table 2-1. MCU Mode Selection Signals

Signal

Function

MODA/MODB

(PD1/PD0)

These two pins are latched at reset to determine the chip mode (See

Table 2-2).

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