PC/104

[phiscock-g851W1bGYuGnS0EtXVNi6w at public.gmane.org]

>> http://www.syscompdesign.com/mppkit.htm
>
> How can anyone call a 68HC11 powerful these days?  Why not go for an
> arm, mips or powerPC instead.  Way more powerful and easier to develop
> for.
>
(Disclaimer: the MPPKit is our design. It's a teaching tool and useful in
some complete systems, but there are better choices for many
applications.)

The arm, mips and powerPC have a very steep learning curve, depending on
what you're trying to do. And they are appropriate for running a complex
program, but not for some simple control tasks.

For example, I recently came across a system where *everything* is
controlled by a central PC board. This required complex multitasking
real-time software running under Linux that was very difficult to debug.
The genius who designed this has of course left the project.  The PC
software included such low-level tasks as operating a stepping motor and
detecting when a shutter is closed.

It's much better to partition the system into low-level tasks that are
handled by microprocessors (not necessarily ours ;). The microprocessors
then communicate with the master PC host via some sort of com link such as
RS232 or CAN bus. So the PC issues a command to 'close the shutter' and
then the microprocessor reports back when the shutter is closed. Very
simple to implement and debug.

In another case, the designers insisted that low-level hardware tasks be
controlled via a PCI interface. The interface hardware is horrendously
complicated  and is going to be a nightmare to debug. A much better
approach would be heirarchical hardware with a PC as the master controller
and microprocessors doing the grunt work.

A microprocessor is about $3 or less these days and anyone reading this
could learn to program one in an hour or two.

-- 
Peter Hiscocks
Syscomp Electronic Design Limited, Toronto
http://www.syscompdesign.com
USB Oscilloscope and Waveform Generator
647-839-0325

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