![](http://datasheet.mmic.net.cn/370000/P312XDP512F0VFV_datasheet_16728159/P312XDP512F0VFV_1233.png)
Chapter 30 Security (S12X9SECV2)
MC9S12XDP512 Data Sheet, Rev. 2.17
Freescale Semiconductor
1233
The meaning of the bits KEYEN[1:0] is shown in
Table 30-2
. Please refer to
Section 30.1.5.1,
“Unsecuring the MCU Using the Backdoor Key Access”
for more information.
The meaning of the security bits SEC[1:0] is shown in
Table 30-3
. For security reasons, the state of device
security is controlled by two bits. To put the device in unsecured mode, these bits must be programmed to
SEC[1:0] = ‘10’. All other combinations put the device in a secured mode. The recommended value to put
the device in secured state is the inverse of the unsecured state, i.e. SEC[1:0] = ‘01’.
NOTE
PleaserefertotheFlashblockguide(FTX)foractualsecurityconfiguration
(in section “Flash Module Security”).
30.1.4
Operation of the Secured Microcontroller
Bysecuringthedevice,unauthorizedaccesstotheEEPROMandFlashmemorycontentscanbeprevented.
However,itmustbeunderstoodthatthesecurityoftheEEPROMandFlashmemorycontentsalsodepends
onthedesignoftheapplicationprogram.Forexample,iftheapplicationhasthecapabilityofdownloading
code through a serial port and then executing that code (e.g. an application containing bootloader code),
then this capability could potentially be used to read the EEPROM and Flash memory contents even when
themicrocontrollerisinthesecurestate.Inthisexample,thesecurityoftheapplicationcouldbeenhanced
by requiring a challenge/response authentication before any code can be downloaded.
Secured operation has the following effects on the microcontroller:
Table 30-2. Backdoor Key Access Enable Bits
KEYEN[1:0]
Backdoor Key
Access Enabled
00
01
10
11
0 (disabled)
0 (disabled)
1 (enabled)
0 (disabled)
Table 30-3. Security Bits
SEC[1:0]
Security State
00
01
10
11
1 (secured)
1 (secured)
0 (unsecured)
1 (secured)