mcf51jf128 Freescale Semiconductor, Inc, mcf51jf128 Datasheet - Page 542

• Manufacturer Part Number: mcf51jf128
• Description: Mcf51jf128 Reference Manual
• Manufacturer: Freescale Semiconductor, Inc

Flash Operation in Low-Power Modes
23.4.12.1 FTFL Access by Mode and Security
The following table summarizes how access to the FTFL module is affected by security
and operating mode.
23.4.12.2 Changing the Security State
The security state out of reset can be permanently changed by programming the security
byte of the flash configuration field. This assumes that you are starting from a mode
where the necessary program flash erase and program commands are available and that
the region of the program flash containing the flash configuration field is unprotected. If
the flash security byte is successfully programmed, its new value takes affect after the
next MCU reset.
23.4.12.2.1 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 8-byte backdoor key value stored in the Flash
Configuration Field (see
bits are in the enabled state, the Verify Backdoor Access Key command (see
Backdoor Access Key
prospective keys for comparison to the stored keys. If the keys match, the FSEC[SEC]
bits are changed to unsecure the MCU. The entire 8-byte key cannot be all 0s or all 1s,
i.e. 0x0000_0000_0000_0000 and 0xFFFF_FFFF_FFFF_FFFF are not accepted by the
Verify Backdoor Access Key command as valid comparison values. While the Verify
Backdoor Access Key command is active, program flash memory is not available for read
access and returns invalid data.
The user code stored in the program flash memory must have a method of receiving the
backdoor keys from an external stimulus. This external stimulus would typically be
through one of the on-chip serial ports.
If the KEYEN bits are in the enabled state, the MCU can be unsecured by the backdoor
key access sequence described below:
542
Operating Mode
NVM Normal
NVM Special
Command) can be run which allows the user to present
MCF51JF128 Reference Manual, Rev. 2, 03/2011
Flash Configuration Field
Table 23-72. FTFL Access Summary
Full command set
Unsecure
Preliminary
MCU Security State
Description). If the FSEC[KEYEN]
Full command set
Only the Erase All Blocks and Read 1s All
Blocks commands.
Freescale Semiconductor, Inc.
Secure
Verify