PC912XDP512F0CFVR datasheet(671/1348 Pages) FREESCALE

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Chapter 18 Memory Mapping Control (S12XMMCV3)

MC9S12XDP512 Data Sheet, Rev. 2.21

Freescale Semiconductor

671

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).

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