Security - NXP Semiconductors MC9S08SU16 Reference Manual

The general guideline is that flash protection can only be added and not removed. The
following table specifies all valid transitions between flash protection scenarios. Any
attempt to write an invalid scenario to the FPROT register will be ignored. The contents
of the FPROT register reflect the active protection scenario. See the FPROT[FPHS] field
descriptions for additional restrictions.
From protection
scenario
1
3
5
7
1. Allowed transitions marked with X.
The flash protection address range is listed in the following two tables regarding the
scenarios in the table above.
Table 11-9. Flash protection higher address range
FPHS[1:0]
00
01
10
11

11.3.8 Security

The flash module provides security information to the MCU. The flash security state is
defined by FSEC[SEC]. During reset, the flash module initializes the FSEC register using
data read from the security byte of the flash configuration field. 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 flash erase and program commands are
available and that the upper region of the flash is unprotected. If the flash security byte is
successfully programmed, its new value will take effect after the next MCU reset.
The following subsections describe these security-related subjects:
• Unsecuring the MCU using backdoor key access
NXP Semiconductors
Table 11-8. Flash protection scenario transitions
1
×
×
Global address range
0xF800–0xFFFF
0xF000–0xFFFF
0xE000–0xFFFF
0xC000–0xFFFF
MC9S08SU16 Reference Manual, Rev. 5, 4/2017
Chapter 11 Flash Memory Module (FTMRH)
1
To protection scenario
3 5
×
×
× ×
× ×
7
×
Protected size
2 KB
4 KB
8 KB
16 KB
165