MC9S12P128 Datasheet, PDF (114/564 Pages) Freescale Semiconductor, Inc – S12 Microcontrollers

S12P Memory Map Control (S12PMMCV1)
This mode is generally used for debugging operation, boot-strapping or security related
operations. The active background debug mode is in control of the CPU code execution and the
BDM firmware is waiting for serial commands sent through the BKGD pin.
3.4.2 Memory Map Scheme
3.4.2.1 CPU and BDM Memory Map Scheme
The BDM firmware lookup tables and BDM register memory locations share addresses with other
modules; however they are not visible in the memory map during user’s code execution. The BDM
memory resources are enabled only during the READ_BD and WRITE_BD access cycles to distinguish
between accesses to the BDM memory area and accesses to the other modules. (Refer to BDM Block
Guide for further details).
When the MCU enters active BDM mode, the BDM firmware lookup tables and the BDM registers
become visible in the local memory map in the range 0xFF00-0xFFFF (global address 0x3_FF00 -
0x3_FFFF) and the CPU begins execution of firmware commands or the BDM begins execution of
hardware commands. The resources which share memory space with the BDM module will not be visible
in the memory map during active BDM mode.
Please note that after the MCU enters active BDM mode the BDM firmware lookup tables and the BDM
registers will also be visible between addresses 0xBF00 and 0xBFFF if the PPAGE register contains value
of 0x0F.
3.4.2.1.1 Expansion of the Local Address Map
Expansion of the CPU Local Address Map
The program page index register in S12PMMC allows accessing up to 256KB of P-Flash in the global
memory map by using the four index bits (PPAGE[3:0]) to page 16x16 KB blocks into the program page
window located from address 0x8000 to address 0xBFFF in the local CPU memory map.
The page value for the program page window is stored in the PPAGE register. The value of the PPAGE
register can be read or written by normal memory accesses as well as by the CALL and RTC instructions
(see Section 3.6.1, “CALL and RTC Instructions).
Control registers, vector space and parts of the on-chip memories are located in unpaged portions of the
64KB local CPU address space.
The starting address of an interrupt service routine must be located in unpaged memory unless the user is
certain that the PPAGE register will be set to the appropriate value when the service routine is called.
However an interrupt service routine can call other routines that are in paged memory. The upper 16KB
block of the local CPU memory space (0xC000–0xFFFF) is unpaged. It is recommended that all reset and
interrupt vectors point to locations in this area or to the other unmapped pages sections of the local CPU
memory map.
S12P-Family Reference Manual, Rev. 1.12
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Freescale Semiconductor