Page 163 - Programming Microcontrollers in C

148 Chapter 3 What Are Microcontrollers?

With BDM, all debug software can be placed on a host computer.
Therefore, it is possible to write much better debugging systems that
connect through the BDM system. Most recent microcontroller chips
employ some type of background debug mode operation. It is not
always called BDM. It might be called ONCE or JTAG, but these
operations are basically similar and allow background debugging of
the microcontroller and a host to contain all of the necessary debug
software.
Another advantage to using the BDM is that all communication
between the host and the device is through an 8-wire bus. This bus
can be accessed in any device, so these devices become their own
development systems and no development system is really needed to
work on the final target system.
The MC68HC16EVB uses the BDM operation. Communications
with the host computer are through the parallel, or printer, port on the
computer. P & E has written an interface for “PC clone” computers that
uses the parallel port. Its operation is essentially as for the
MC68HC05EVM and MC68HC11EVM devices. P & E has also made
an additional device which can connect to the 8-wire BDM bus and
connect directly to the host computer parallel port. It requires a +5 volt
power source and takes its voltage through the lines to the target system.
Three other chips will be examined in the following chapters. The
M68HC08 family and the M68HC12 family are extensions of the
M68HC05 and the M68HC11 families, respectively. Yet another recent
chip family is the MCORE. These RISC chips are very fast and run at
extremely low power. The MMC2001 chip from this family will be
examined. The development system for the MCORE chips is called an
EBDI—Extended Background Debug Interface. This package is
interfaced to an evaluation board through an 8-wire serial port.
All of the programs in the chapters that follow were tested on the
appropriate development boards. These programs are relatively small
because each is designed to show some feature of either the
microcontroller or the language as applied to the microcontroller; larger
programs were not appropriate to the tutorial aims of this book. With
judicious use of the boards along with the development environment
on the host computer, these programs were easy to develop and debug.