Freescale Semiconductor, Inc.
Operating Modes and Resource Mapping
Special Expanded Narrow Mode — This mode can be used
for emulation of normal expanded narrow mode. 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.
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.
5.4 Background Debug Mode
Background debug mode (BDM) is an auxiliary operating mode that is
used for system development. BDM is implemented in on-chip hardware
and provides a full set of debug operations. Some BDM commands can
be executed while the CPU is operating normally. Other BDM
commands are firmware based, and require the BDM firmware to be
enabled and active for execution.
In special single-chip mode, BDM is enabled and active immediately out
of reset. BDM is available in all other operating modes, but must be
enabled before it can be activated. BDM should not be used in special
peripheral mode because of potential bus conflicts.
Once enabled, background mode can be made active by a serial
command sent via the BKGD pin or execution of a CPU12 BGND
instruction. While background mode is active, the CPU can interpret
special debugging commands, and read and write CPU registers,
peripheral registers, and locations in memory.
While BDM is active, the CPU executes code located in a small on-chip
ROM mapped to addresses $FF20 to $FFFF, and BDM control registers
are accessible at addresses $FF00 to $FF06. The BDM ROM replaces
Advance Information
76
68HC(9)12D60 — Rev 4.0
Operating Modes and Resource Mapping
MOTOROLA
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA [ MOTOROLA ]
