
Chapter 18 Memory Mapping Control (S12XMMCV3)
MC9S12XDP512 Data Sheet, Rev. 2.17
Freescale Semiconductor
687
18.5.3
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.
18.5.3.1
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 18-27
).
Figure 18-27. ROM in Single Chip Modes
18.5.3.2
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,
theinternalFLASHprovidesthedataandtheemulatorcanobserveallinternalCPUactionsontheexternal
bus. If the EROMON bit is cleared, the emulator provides the data (generator) and traces the all CPU
actions (see
Figure 18-28
).
Figure 18-28. ROM in Emulation Single-Chip Mode
MCU
Flash
No External Bus
EROMON = 1
Emulator
MCU
EROMON = 0
Emulator
Flash
MCU
Flash
Observer
Generator