HCS08 datasheet(50/374 Pages) NXP

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Chapter 4 Memory

MC9S08JM60 Series Data Sheet, Rev. 5

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

Address

Bit 7

Bit 0

0xFFAE

Reserved for

storage of FTRIM

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

SEC01

SEC00

Table 4-3. High-Page Register Summary (Sheet 3 of 3)

Address

Bit 7

Bit 0

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