MC3S12RG128 Datasheet, PDF (438/546 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 15 Read-Only Memory 64K x 16 (ROM64KX16V1) Block Description
Table 15-2. ROPT Field Descriptions
Field
Description
7−6
Key Enable Bits — Backdoor Key Mechanism Enable. The KEYEN[1:0] bits control backdoor key access to the
KEYEN[1:0] ROM module as shown in Table 15-3. If the backdoor key mechanism is enabled, user firmware can write a
4-words value that matches the non-volatile backdoor key (NVBACKKEY+0x0000 through
NVBACKKEY+0x0007 in that order), to temporarily disengage security until the next reset. The backdoor key
mechanism is accessible only from user (secured) firmware. BDM commands cannot be used to write key
comparison values that would unlock the backdoor key.
If disabled, no backdoor key access allowed.
Note: Please note that backdoor keywords $0000 and $FFFF are invalid and will effectively disable backdoor key
access when used.
Note: On Mask-ROM devices the backdoor key is also used to protect access to internal product analysis
features. No product analysis will be possible on a secured ROM if backdoor key access is disabled or
keywords are invalid.
5−2
Non-Volatile Flag Bits — These 4 bits are available to the user as non-volatile flags.
NV[5:2]
1−0
Security State Code — This 2-bit field determines the security state of the MCU. The security state is coded as
SEC[1:0] shown in Table 15-4.
Table 15-3. ROM Backdoor Key Enable States
KEYEN[1:0]
Status of Backdoor Key Access
00
Disabled
01
Disabled¹
10
Enabled
11
Disabled
1_{Preferred KEYEN state to disable Backdoor Key Access.}
Table 15-4. ROM Security States
SEC[1:0]
Status of Security
00
Secured
01
Secured¹
10
Unsecured
11
Secured
1 _{Preferred SEC state to secure the MCU.}
MC3S12RG128 Data Sheet, Rev. 1.05
438
Freescale Semiconductor