MC68HC812A4 Datasheet, PDF (82/342 Pages) Motorola, Inc – 16-bit device composed of standard on-chip peripheral modules connected by an intermodule bus. Modules include

Operating Modes and Resource Mapping
5.3.2 Special Operating Modes
Special operating modes are commonly used in factory testing and
system development.
5.3.2.1 Special Expanded Wide Mode
This mode is for emulation of normal expanded wide mode and
emulation of normal single-chip mode with a 16-bit bus. The bus-control
pins of port E are all configured for their bus-control output functions
rather than general-purpose I/O.
5.3.2.2 Special Expanded Narrow Mode
This mode is for emulation of normal expanded narrow mode. External
16-bit data is handled as two back-to-back bus cycles, one for the high
byte followed by one for the low byte. Internal operations continue to use
full 16-bit data paths.
For development purposes, port D can be made available for visibility of
16-bit internal accesses by setting the EMD and IVIS control bits.
5.3.2.3 Special Single-Chip Mode
This mode can be used to force the MCU to active BDM mode to allow
system debug through the BKGD pin. There are no external address and
data buses in this mode. The MCU operates as a stand-alone device
and all program and data space are on-chip. External port pins can be
used for general-purpose I/O.
5.3.2.4 Special Peripheral Mode
The CPU is not active in this mode. An external master can control
on-chip peripherals for testing purposes. It is not possible to change to
or from this mode without going through reset. Background debugging
should not be used while the MCU is in special peripheral mode as
internal bus conflicts between BDM and the external master can cause
improper operation of both modes.
MC68HC812A4 — Rev. 3.0
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Operating Modes and Resource Mapping
Advance Information
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