Chapter 1 Device Overview MC9S12ZVHY/MC9S12ZVHL Families
S12ZVHY/S12ZVHL Family Reference Manual Rev. 1.05
Freescale Semiconductor
61
NOTE
Please refer to the
for more security byte details.
1.10.3
Operation of the Secured Microcontroller
By securing the device, unauthorized access to the EEPROM and Flash memory contents is prevented.
Secured operation has the following effects on the microcontroller:
1.10.3.1
Normal Single Chip Mode (NS)
•
Background Debug Controller (BDC) operation is completely disabled.
•
Execution of Flash and EEPROM commands is restricted (described in flash block description).
1.10.3.2
Special Single Chip Mode (SS)
•
Background Debug Controller (BDC) commands are restricted
•
Execution of Flash and EEPROM commands is restricted (described in flash block description).
In special single chip mode the device is in active BDM after reset. In special single chip mode on a secure
device, only the BDC mass erase and BDC control and status register commands are possible. BDC access
to memory mapped resources is disabled. The BDC can only be used to erase the EEPROM and Flash
memory without giving access to their contents.
1.10.4
Unsecuring the Microcontroller
Unsecuring the microcontroller can be done using three different methods:
1. Backdoor key access
2. Reprogramming the security bits
3. Complete memory erase
1.10.4.1
Unsecuring the MCU Using the Backdoor Key Access
In normal single chip mode, security can be temporarily disabled using the backdoor key access method.
This method requires that:
•
The backdoor key has been programmed to a valid value.
•
The KEYEN[1:0] bits within the Flash options/security byte select ‘enabled’.
Table 1-9. Security Bits
SEC[1:0]
Security State
00
1 (secured)
01
1 (secured)
10
0 (unsecured)
11
1 (secured)
