Datasheet

MC9S12G Family Reference Manual, Rev.1.23
Freescale Semiconductor 355
Chapter 9
Security (S12XS9SECV2)
9.1 Introduction
This specification describes the function of the security mechanism in the MC9S12G-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
The user must be reminded that part of the security must lie with the application code. An extreme example
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 MC9S12G-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)
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
Revision
Number
Revision
Date
Sections
Affected
Description of Changes
02.00 27 Aug 2004 reviewed and updated for S12XD architecture
02.01 21 Feb 2007 added S12XE, S12XF and S12XS architectures
02.02 19 Apr 2007 corrected statement about Backdoor key access via BDM on XE, XF, XS
Table 9-2. Feature Availability in Unsecure and Secure Modes on S12XS
Unsecure Mode Secure Mode
NS SS NX ES EX ST NS SS NX ES EX ST
Flash Array Access ✔✔
✔✔