NXP Semiconductors MC9S08LG16, Reference Manual

Page: 60 / 373

Chapter 4 Memory
MC9S08LG32 MCU Series, Rev. 5
60 Freescale Semiconductor
debug interface) and verifying that flash is blank. To avoid returning to secure mode after the next reset,
program the security bits (SEC) to the unsecured state (1:0).
4.5 RAM
The MC9S08LG32 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.
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 (V
RAM
).
For compatibility with M68HC05 MCUs, the HCS08 resets the stack pointer to 0x00FF. In the
MC9S08LG32 series, it is usually best to reinitialize 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 Semiconductor-provided equate file).
LDHX #1 ;point one past RAM
TXS ;SP<-(H:X-1)
When security is enabled, the RAM is considered a secure memory resource and is not accessible through
background debug mode (BDM) or through code executing from non-secure memory. See
Section 4.7,
“Security ,” for a detailed description of the security feature.
4.6 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
to program the entire array through the single-wire background debug interface. Because no special
voltages are needed for flash erase and programming operations, in-application programming is also
possible through other software-controlled communication paths. For a more detailed discussion of
in-circuit and in-application programming, refer to the
HCS08 Family Reference Manual, Volume I,
Freescale Semiconductor document order number HCS08RMv1/D.
Because the MC9S08LG32 series contains two flash arrays, program and erase operations can be
conducted on one array while executing code from the other. The security and protection features treat the
two arrays as a single memory entity. Programming and erasing of each flash array is conducted through
the same command interface detailed in the following sections.
It is not possible to page erase or program both arrays at the same time. The mass erase command erases
both arrays, and the blank check command checks both arrays.