Freescale Semiconductor, Inc.
Operating Modes
Operating Modes
Normal Single-Chip Mode — There are no external address
and data buses in this mode. The MCU operates as a stand-
alone device and all program and data resources are on-chip.
External port pins normally associated with address and data
buses can be used for general-purpose I/O.
Normal Expanded Wide Mode — This is a normal mode of
operation in which the expanded bus is present with a 16-bit
data bus. Ports A and B are used for the 16-bit multiplexed
address/data bus.
Normal Expanded Narrow Mode — This is a normal mode of
operation in which the expanded bus is present with an 8-bit
data bus. Ports A and B are used for the16-bit address bus.
Port A is used as the data bus, multiplexed with addresses. In
this mode, 16-bit data is presented one byte at a time, the high
byte followed by the low byte. The address is automatically
incremented on the second cycle.
5.3.2 Special Operating Modes
There are three special operating modes that correspond to normal
operating modes. These operating modes are commonly used in factory
testing and system development. In addition, there is a special
peripheral mode, in which an external master, such as an I.C. tester, can
control the on-chip peripherals.
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.
Special Expanded Wide Mode — This mode can be used for
emulation of normal expanded wide mode and emulation of
normal single-chip mode. Ports A and B are used for the 16-bit
multiplexed address/data bus.
MC68HC912DG128 — Rev 3.0
Technical Data
Operating Modes
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