Datasheet

Operating Modes
Technical Data MC68HC912DT128A — Rev 4.0
80 Operating Modes MOTOROLA
There are two basic types of operating modes:
Normal modes — some registers and bits are protected
against accidental changes.
Special
modes — allow greater access to protected control
registers and bits for special purposes such as testing and
emulation.
A system development and debug feature, background debug mode
(BDM), is available in all modes. In special single-chip mode, BDM is
active immediately after reset.
5.3.1 Normal Operating Modes
These modes provide three operating configurations. Background
debug is available in all three modes, but must first be enabled for some
operations by means of a BDM background command, then activated.
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.
Table 5-1. Mode Selection
BKGD MODB MODA Mode Port A Port B
1 0 0 Normal Single Chip G.P. I/O G.P. I/O
1 0 1 Normal Expanded Narrow ADDR/DATA ADDR
1 1 0 Reserved (Forced to Peripheral) — —
1 1 1 Normal Expanded Wide ADDR/DATA ADDR/DATA
0 0 0 Special Single Chip G.P. I/O G.P. I/O
0 0 1 Special Expanded Narrow ADDR/DATA ADDR
0 1 0 Special Peripheral ADDR/DATA ADDR/DATA
0 1 1 Special Expanded Wide ADDR/DATA ADDR/DATA
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cale Semiconductor,
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