MC912DG128A Motorola, MC912DG128A Datasheet - Page 64

• Manufacturer Part Number: MC912DG128A
• Description: Microcontrollers
• Manufacturer: Motorola

Normal Operating
Modes
Operating Modes
MC68HC912DT128A Rev 2.0
64
BKGD
0
0
MODB
1
1
MODA
There are two basic types of operating modes:
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.
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.
0
1
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.
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.
Table 9 Mode Selection
Special Expanded Wide
Special Peripheral
Operating Modes
Mode
ADDR/DATA
ADDR/DATA
Port A
ADDR/DATA
ADDR/DATA
Port B
MOTOROLA
2--modes