MC9S12T64 Datasheet, PDF (118/608 Pages) Motorola, Inc – Specification

Freescale Semiconductor, Inc.
Operating Modes
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 user downloads a “key” through the
SCI which allows access to a programming routine that updates
parameters stored in Flash EEPROM.
Securing the
Microcontroller
Once the user has programmed the FLASH, the part can be secured by
programming the security bits located in the FLASH module. These
non-volatile bits will keep the part secured through resetting the part and
through powering down the part.
The security byte resides in a portion of the Flash array.
Two bits are used for security. The state of the security bits and the
resulting state of security are shown in Table 22. Note that there are
three secured bit combinations and only one unsecured combination.
The user can select any of the three combinations to secure the
microcontroller.
Table 22 : Security Bits
sec1
0
0
1
1
sec0
0
1
0
1
secreq
1 (secured)
1 (secured)
0 (unsecured)
1 (secured)
NOTE:
When the MCU is in the secured state and in the special single chip
mode, reading the CALRAM array returns $FFFF for any word accesses
or $FF for any byte accesses.
CAUTION: Check the Flash section for more details on the security configuration.
MC9S12T64Revision 1.1.1
Operating Modes
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