Datasheet

Chapter 4 Memory
MC9S08JM60 Series Data Sheet, Rev. 3
50 Freescale Semiconductor
Nonvolatile flash registers, shown in Table 4-4, are located in the flash memory. These registers include
an 8-byte backdoor key which optionally can be used to gain access to secure memory resources. During
reset events, the contents of NVPROT and NVOPT in the nonvolatile register area of the flash memory
are transferred into corresponding FPROT and FOPT working registers in the high-page registers to
control security and block protection options.
Provided the key enable (KEYEN) bit is 1, the 8-byte comparison key can be used to temporarily
disengage memory security. This key mechanism can be accessed only through user code running in secure
memory. (A security key cannot be entered directly through background debug commands.) This security
key can be disabled completely by programming the KEYEN bit to 0. If the security key is disabled, the
only way to disengage security is by mass erasing the flash if needed (normally through the background
debug interface) and verifying that flash is blank. To avoid returning to secure mode after the next reset,
program the security bits (SEC01:SEC00) to the unsecured state (1:0).
4.3 RAM (System RAM)
The MC9S08JM60 series includes static RAM. The locations in RAM below 0x0100 can be accessed
using the more efficient direct addressing mode, and any single bit in this area can be accessed with the bit
manipulation instructions (BCLR, BSET, BRCLR, and BRSET). Locating the most frequently accessed
program variables in this area of RAM is preferred.
0x1857 Reserved — — — — — — — —
0x1858 PTGPE — — PTGPE5 PTGPE4 PTGPE3 PTGPE2 PTGPE1 PTGPE0
0x1859 PTGSE
— — PTGSE5 PTGSE4 PTGSE3 PTGSE2 PTGSE1 PTGSE0
0x185A PTGDS — — PTGDS5 PTGDS4 PTGDS3 PTGDS2 PTGDS1 PTGDS0
0x185B–
0x185F
Reserved
— — — — — — — —
1
This reserved bit must always be written to 0.
Table 4-4. Nonvolatile Register Summary
AddressRegister NameBit 7654321Bit 0
0xFFAE Reserved for
storage of FTRIM
0 0 0 0 0 0 0FTRIM
0xFFAF Res. for storage of
MCGTRIM
TRIM
0xFFB0–
0xFFB7
NVBACKKEY 8-Byte Comparison Key
0xFFB8–
0xFFBC
Reserved
— — — — — — — —
0xFFBD NVPROT FPS7 FPS6 FPS5 FPS4 FPS3 FPS2 FPS1 FPDIS
0xFFBE Reserved — — — — — — — —
0xFFBF NVOPT KEYEN FNORED 0 0 0 0 SEC01 SEC00
Table 4-3. High-Page Register Summary (Sheet 3 of 3)
AddressRegister NameBit 7654321Bit 0