MC9S12GRMV1 Datasheet, PDF (1029/1292 Pages) Freescale Semiconductor, Inc – MC9S12G Family Reference Manual and Data Sheet

96 KByte Flash Module (S12FTMRG96K1V1)
28.4.8 Wait Mode
The Flash module is not affected if the MCU enters wait mode. The Flash module can recover the MCU
from wait via the CCIF interrupt (see Section 28.4.7, “Interrupts”).
28.4.9 Stop Mode
If a Flash command is active (CCIF = 0) when the MCU requests stop mode, the current Flash operation
will be completed before the MCU is allowed to enter stop mode.
28.5 Security
The Flash module provides security information to the MCU. The Flash security state is defined by the
SEC bits of the FSEC register (see Table 28-11). During reset, the Flash module initializes the FSEC
register using data read from the security byte of the Flash configuration field at global address 0x3_FF0F.
The security state out of reset can be permanently changed by programming the security byte assuming
that the MCU is starting from a mode where the necessary P-Flash erase and program commands are
available and that the upper region of the P-Flash is unprotected. If the Flash security byte is successfully
programmed, its new value will take affect after the next MCU reset.
The following subsections describe these security-related subjects:
• Unsecuring the MCU using Backdoor Key Access
• Unsecuring the MCU in Special Single Chip Mode using BDM
• Mode and Security Effects on Flash Command Availability
28.5.1 Unsecuring the MCU using Backdoor Key Access
The MCU may be unsecured by using the backdoor key access feature which requires knowledge of the
contents of the backdoor keys (four 16-bit words programmed at addresses 0x3_FF00-0x3_FF07). If the
KEYEN[1:0] bits are in the enabled state (see Section 28.3.2.2), the Verify Backdoor Access Key
command (see Section 28.4.6.11) allows the user to present four prospective keys for comparison to the
keys stored in the Flash memory via the Memory Controller. If the keys presented in the Verify Backdoor
Access Key command match the backdoor keys stored in the Flash memory, the SEC bits in the FSEC
register (see Table 28-11) will be changed to unsecure the MCU. Key values of 0x0000 and 0xFFFF are
not permitted as backdoor keys. While the Verify Backdoor Access Key command is active, P-Flash
memory and EEPROM memory will not be available for read access and will return invalid data.
Freescale Semiconductor
MC9S12G Family Reference Manual, Rev.1.23
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