
MC9S12XE-Family Reference Manual , Rev. 1.07
Freescale Semiconductor
347
Chapter 9
Security (S12XE9SECV2)
9.1
Introduction
This specification describes the function of the security mechanism in the S12XE chip family (9SEC).
NOTE
No security feature is absolutely secure. However, Freescale’s strategy is to
make reading or copying the FLASH and/or EEPROM difficult for
unauthorized users.
9.1.1
Features
Theusermustberemindedthatpartofthesecuritymustliewiththeapplicationcode.Anextremeexample
would be application code that dumps the contents of the internal memory. This would defeat the purpose
of security. At the same time, the user may also wish to put a backdoor in the application program. An
example of this is the user downloads a security key through the SCI, which allows access to a
programming routine that updates parameters stored in another section of the Flash memory.
The security features of the S12XE chip family (in secure mode) are:
Protect the content of non-volatile memories (Flash, EEPROM)
Execution of NVM commands is restricted
Disable access to internal memory via background debug module (BDM)
Disable access to internal Flash/EEPROM in expanded modes
Disable debugging features for the CPU and XGATE
9.1.2
Modes of Operation
Table 9-2
gives an overview over availability of security relevant features in unsecure and secure modes.
Table 9-1. Revision History
Version
Number
Revision
Date
Effective
Date
Author
Description of Changes
02.00
27 Aug
2004
21 Feb
2007
19 Apr
2007
08 Sep
2004
21 Feb
2007
19 Apr
2007
reviewed and updated for S12XD architecture
02.01
added S12XE, S12XF and S12XS architectures
02.02
correctedstatementaboutBackdoorkeyaccessviaBDMonXE,XF,
XS