Hardware Reference
In-Depth Information
PAD1
PAD0
Operating Mode
0
0
1
1
0
1
0
1
D-Bug12; EVB
Jump to internal EEPROM
D-Bug12; POD
SerialBootloader
Table 3.1
■
D-Bug12 operating modes
The EVB mode is the most important mode for beginners to learn the HCS12 microcon-
troller using a demo board. In this mode, the monitor operates as a ROM resident monitor/
debugger executing from the on-chip flash memory. Although this mode provides a good envi-
ronment for testing new algorithms or conducting performance benchmarks, it does have a few
limitations. In this mode, the flash memory, 1024 bytes of on-chip SRAM, and one of the SCI
serial ports are not available to the developer. The portion of the SRAM that may be used by the
user program begins at $1000 and ends at $3BFF. D-Bug12 uses the remainder of the SRAM that
begins at $3C00 and ends at $3FFF. User programs can also be loaded onto the on-chip EEPROM
for execution. The conceptual operating model for this mode is illustrated in Figure 3.3.
HCS12 demo board
PC running
a terminal
program
Low-level
interface
routines
Target
system
D-Bug12
User
Figure 3.3
■
EVB mode conceptual model
Suppose we have run a terminal program on the PC and selected the EVB mode; then either
powering on the demo board or pressing the reset button brings out the sign-on message shown
in Figure 3.4 on the terminal screen. The D-Bug12 monitor displays the ASCII greater than
character (.), indicating that it is ready to accept a command. When issuing a command that
causes a program to run from the internal RAM or EEPROM, D-Bug12 will place the terminal
cursor on a blank line, where it will remain until control is returned to D-Bug12. If a running
program fails to return to D-Bug12, pressing the EVB's reset button causes the running program
to halt execution and initiate the D-Bug12 initialization sequence. Using this method to regain
control of an executing program fails to report any information to the programmer on why or
how the program may have failed.
D-Bug12 4.0.0b32
Copyright 1996-2005 Motorola Semiconductor
For Commands type "Help"
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Figure 3.4
■
D-Bug12 EVB mode sign on message
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