Operating Modes; Flash Module Security - ROHS MC9S08QE128 Reference Manual

Chapter 4 Memory
4.6.4

Operating Modes

4.6.4.1 Wait Mode
If a command is active (FCCF = 0) when the MCU enters wait mode, the active command and any buffered
command will be completed.
4.6.4.2 Stop Mode
If a command is active (FCCF = 0) when the MCU enters stop mode, the operation will be aborted and, if
the operation is program or erase, the flash array data being programmed or erased may be corrupted and
the FCCF and FACCERR flags will be set. If active, the high voltage circuitry to the flash array will
immediately be switched off when entering stop mode. Upon exit from stop mode, the FCBEF flag is set
and any buffered command will not be launched. The FACCERR flag must be cleared before starting a
command write sequence (see
As active commands are immediately aborted when the MCU enters stop
mode, it is strongly recommended that the user does not use the STOP
instruction during program or erase operations.
4.6.4.3 Background Debug Mode
In background debug mode (BDM), the FPROT register is writable. If the MCU is unsecured, then all flash
commands listed in Table 4-23
4.6.5

Flash Module Security

The MC9S08QE128 Series includes circuitry to prevent unauthorized access to the contents of flash and
RAM memory. When security is engaged, flash and RAM are considered secure resources. Direct-page
registers, high-page registers, and the background debug controller are considered unsecured resources.
Programs executing within secure memory have normal access to any MCU memory locations and
resources. Attempts to access a secure memory location with a program executing from an unsecured
memory space or through the background debug interface are blocked (writes are ignored and reads return
all 0s).
The flash module provides the necessary security information to the MCU. During each reset sequence,
the flash module determines the security state of the MCU as defined in
Register (FOPT and NVOPT)".
The contents of the flash security byte in NVOPT must be changed directly by programming the NVOPT
location when the MCU is unsecured and the sector containing NVOPT is unprotected. If NVOPT is left
in a secured state, any reset will cause the MCU to initialize into a secure operating mode.
The on-chip debug module cannot be enabled while the MCU is secure. The separate background debug
controller can still be used for background memory access commands of unsecured resources.
86
Section 4.6.3.1.2, "Command Write
NOTE
can be executed.
MC9S08QE128 MCU Series Reference Manual, Rev. 2
Sequence").
Section 4.6.2.2, "Flash Options
Freescale Semiconductor