NXP Semiconductors MC9S08LG16, Reference Manual

Page: 70 / 373

Chapter 4 Memory
MC9S08LG32 MCU Series, Rev. 5
70 Freescale Semiconductor
4.8.3 Flash Configuration Register (FCNFG)
4.8.4 Flash Protection Register (FPROT and NVPROT)
During reset, the contents of the nonvolatile location NVPROT is copied from flash into FPROT. FPROT
can be read at any time. With FPDIS set, all bits are writable, but with FPDIS clear the FPS bits are writable
as long as the size of the protected region is being increased. Any FPROT write that attempts to decrease
the size of the protected region is ignored.
Figure 4-8. Flash Protection Register (FPROT)
Table 4-10. Security States
1
1
SEC01:SEC00 changes to 1:0 after successful backdoor
key entry or a successful blank check of flash.
SEC01:SEC00 Description
0:0 secure
0:1 secure
1:0 unsecured
1:1 secure
7 6 5 4 3 2 1 0
R 0 0
KEYACC
0 0 0 0 0
W
Reset 0 0 0 0 0 0 0 0
= Unimplemented or Reserved
Figure 4-7. Flash Configuration Register (FCNFG)
Table 4-11. FCNFG Register Field Descriptions
Field Description
5
KEYACC
Enable Writing of Access Key — This bit enables writing of the backdoor comparison key. For more detailed
information about the backdoor key mechanism, refer to Section 4.7, “Security .”
0 Writes to flash are interpreted as the start of a flash programming or erase command.
1 Writes to NVBACKKEY (0xFFB0–0xFFB7) are interpreted as comparison key writes while writes to rest of the
flash are ignored.
7 6 5 4 3 2 1 0
R
FPS
(1)
1
Background commands can be used to change the contents of these bits in FPROT.
FPDIS
(1)
W
Reset This register is loaded from nonvolatile location NVPROT during reset.