MC9S12XD256MAL Datasheet, PDF (671/1348 Pages) Freescale Semiconductor, Inc – Freescale’s Scalable Controller Area Network

Chapter 18 Memory Mapping Control (S12XMMCV3)
18.4 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.
18.4.1 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.
• Emulation single-chip mode
Tool vendors use this mode for emulation systems in which the user’s target application is normal
single-chip mode. Code is executed from external or internal memory depending on the set-up of
the EROMON bit (see Section 18.3.2.5, “MMC Control Register (MMCCTL1)). The external bus
is active in both cases to allow observation of internal operations (internal visibility).
MC9S12XDP512 Data Sheet, Rev. 2.21
Freescale Semiconductor
671