Freescale Semiconductor HCS08 Series, Reference Manual

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Chapter 4 Memory
MC9S08JS16 MCU Series Reference Manual, Rev. 4
38 Freescale Semiconductor
• Direct-page registers are located in the first 128 locations in the memory map, so they are
accessible with efficient direct addressing mode instructions.
• High-page registers are used much less often, so they are located above 0x1800 in the memory
map. This leaves more room in the direct-page for more frequently used registers and variables.
• The nonvolatile register area consists of a block of 16 locations in flash memory at
0xFFB0–0xFFBF.
Nonvolatile register locations include:
— Three values that are loaded into working registers at reset
— An 8-byte backdoor comparison key that optionally allows a user to gain controlled access to
secure memory
Because the nonvolatile register locations are flash memory, they must be erased and programmed
like other flash memory locations.
Direct-page registers can be accessed with efficient direct addressing mode instructions. Bit manipulation
instructions can be used to access any bit in any direct-page register.
Table 4-2 is a summary of all
user-accessible direct-page registers and control bits.
The direct-page registers in Table 4-2 can use the more efficient direct addressing mode that requires only
the lower byte of the address. Because of this, the lower byte of the address in column one is shown in bold
text. In
Table 4-3 and Table 4-4 the whole address in column one is shown in bold. In Table 4-2 , Table 4-3 ,
and Table 4-4 , the register names in column two are shown in bold to set them apart from the bit names to
the right. Cells that are not associated with named bits are shaded. A shaded cell with a 0 indicates this
unused bit always reads as a 0. Shaded cells with dashes indicate unused or reserved bit locations that could
read as 1s or 0s.