PXS20RM Datasheet, PDF (135/1368 Pages) Freescale Semiconductor, Inc – PXS20 Microcontroller

Chapter 6
Device Security
Device Security
6.1 Security
The censorship mechanism implemented on the device is intended to increase the protection against
unauthorized access to the device. The mechanisms employed does not provide a guarantee of a secure
device. It can only be deemed effective if used in conjunction with an appropriately robust software and
documentation infrastructure to assist in guarding against unauthorized access to device resources.
When the flash memory is censored, the MCU is in the Secured state. This feature intends to prevent the
unauthorized read and write of memory contents. Which device features are enabled or disabled is
determined by the chip mode and security state in effect. Please refer to Section 5.4, Device behavior by
boot mode, for details.
The user needs to keep in mind that part of the security must lie with the application code. As an extreme
example: it would be possible to generate application code that dumps the contents of the internal program
- obviously this code would defeat the purpose of security. However there may be good reasons to provide
a back door in the application code. Care must be taken when implementing these backdoors, since they
allow paths of attack to break security on the device.
6.1.1 Securing the microcontroller
The device can be secured by programming the flash memory NVSCI register (Figure 6-1; also see
Section 23.1.6.15, Nonvolatile System Censoring Information register (NVSCI)). This non-volatile
register will keep the device secured even when it is reset or powered down.
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
R
Censorship Control
W
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
R
Serial Boot Control
W
Figure 6-1. Nonvolatile System Censorship Information Register (NVSCI) for cut1
PXS20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor
6-1