Chapter 23 Memory Mapping Control (S12XMMCV2)
MC9S12XDP512 Data Sheet, Rev. 2.11
914 Freescale Semiconductor
23.5.3 On-Chip ROM Control
The MCU offers two modes to support emulation. In the first mode (called generator) the emulator
provides the data instead of the internal FLASH and traces the CPU actions. In the other mode (called
observer) the internal FLASH provides the data and all internal actions are made visible to the emulator.

23.5.3.1 ROM Control in Single-Chip Modes

In single-chip modes the MCU has no external bus. All memory accesses and program fetches are internal
(see Figure 1-27).
Figure 23-27. ROM in Single Chip Modes

23.5.3.2 ROM Control in Emulation Single-Chip Mode

In emulation single-chip mode the external bus is connected to the emulator. If the EROMON bit is set,
the internal FLASH provides the data and the emulator can observe all internal CPU actions on the external
bus. If the EROMON bit is cleared, the emulator provides the data (generator) and traces the all CPU
actions (see Figure 1-28).
Figure 23-28. ROM in Emulation Single-Chip Mode
MCU
Flash
No External Bus
EROMON = 1
Emulator
MCU
EROMON = 0
Emulator
Flash
MCU
Flash
Observer
Generator