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MC9S08AW60 Datasheet(PDF) 49 Page - Freescale Semiconductor, Inc

No. de Pieza. MC9S08AW60
Descripción  Microcontrollers
Descarga  324 Pages
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Fabricante  FREESCALE [Freescale Semiconductor, Inc]
Página de inicio  http://www.freescale.com
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MC9S08AW60 Datasheet(HTML) 49 Page - Freescale Semiconductor, Inc

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Chapter 4 Memory
MC9S08AW60 Data Sheet, Rev 2
Freescale Semiconductor
49
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 MC9S08AW60 Series includes static RAM. The locations in RAM below $0100 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, 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 $00FF. In the
MC9S08AW60 Series, 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
#RamLast+1
;point one past RAM
TXS
;SP<-(H:X-1)
Table 4-4. Nonvolatile Register Summary
Address
Register Name
Bit 7
654321
Bit 0
$FFB0 –
$FFB7
NVBACKKEY
8-Byte Comparison Key
$FFB8 –
$FFBB
Reserved
$FFBC
Reserved for stor-
age of 250 kHz
ICGTRM value
$FFBD
NVPROT
FPS7
FPS6
FPS5
FPS4
FPS3
FPS2
FPS1
FPDIS
$FFBE
Reserved for stor-
age of 243 kHz
ICGTRM value
$FFBF
NVOPT
KEYEN
FNORED
0
0
0
0
SEC01
SEC00


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