MC9S08GB60A Datasheet, PDF (50/302 Pages) Freescale Semiconductor, Inc – HCS08 Microcontrollers

Chapter 4 Memory
Table 4-4. Nonvolatile Register Summary
Address Register Name Bit 7
6
5
4
3
2
0xFFB0 – NVBACKKEY
0xFFB7
8-Byte Comparison Key
0xFFB8 – Reserved
0xFFBC
—
—
—
—
—
—
—
—
—
—
—
—
0xFFBD NVPROT
0xFFBE Reserved¹
FPOPEN FPDIS
FPS2
FPS1
FPS0
0
—
—
—
—
—
—
0xFFBF NVOPT
KEYEN FNORED
0
0
0
0
1 _{This location is used to store the factory trim value for the ICG.}
1
Bit 0
—
—
0
—
SEC01
—
—
0
—
SEC00
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
The MC9S08GBxxA/GTxxA 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.
The RAM retains data when the MCU is in low-power wait, stop2, or stop3 mode. At power-on or after
wakeup from stop1, the contents of RAM are uninitialized. RAM data is unaffected by any reset provided
that the supply voltage does not drop below the minimum value for RAM retention.
For compatibility with older M68HC05 MCUs, the HCS08 resets the stack pointer to 0x00FF. In the
MC9S08GBxxA/GTxxA, it is usually best to re-initialize the stack pointer to the top of the RAM so the
direct page RAM can be used for frequently accessed RAM variables and bit-addressable program
variables. Include the following 2-instruction sequence in your reset initialization routine (where RamLast
is equated to the highest address of the RAM in the Freescale-provided equate file).
LDHX
TXS
#RamLast+1
;point one past RAM
;SP<-(H:X-1)
When security is enabled, the RAM is considered a secure memory resource and is not accessible through
BDM or through code executing from non-secure memory. See Section 4.5, “Security” for a detailed
description of the security feature.
4.4 Flash
The flash memory is intended primarily for program storage. In-circuit programming allows the operating
program to be loaded into the flash memory after final assembly of the application product. It is possible
MC9S08GB60A Data Sheet, Rev. 2
50
Freescale Semiconductor