Memory Mapping Control (S12XMMCV4)
MC9S12XHY-Family Reference Manual, Rev. 1.01
170
Freescale Semiconductor
3.4
Functional Description
The MMC block performs several basic functions of the S12X sub-system operation: MCU operation
modes, priority control, address mapping, select signal generation and access limitations for the system.
Each aspect is described in the following subsections.
3.4.1
MCU Operating Mode
•
Normal single-chip mode
There is no external bus in this mode. The MCU program is executed from the internal memory
and no external accesses are allowed.
•
Special single-chip mode
This mode is generally used for debugging single-chip 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. There is no external
bus in this mode.
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 global 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 0x7F_FF00 -
0x7F_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 global 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 0xFF.
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