Volume 2, Number 11 Copyright 1997 TGG December 1, 1997

EDITOR: Jack Ganssle, jack@ganssle.com

CONTENTS:
- Editor's Notes
- History of Electronics Article
- More Dumb Mistakes
- Embedded Seminar in Washington DC
- Thought for the Week
- About The Embedded Muse

Editor's Notes

I’ve received a number of requests to do my “The Best Ideas for Developing Better Firmware Faster” seminar in the DC area, so have scheduled a class there on January 29. More info follows in this newsletter.

Finally, in reaction to The Embedded Muse 10’s comments about Windows CE, I received a **lot** of email from those who love and those who hate the idea of embedded CE. Of those that dislike the idea, about half are Microsoft-haters; the rest worry about the resources required to support such a complex OS. For a number of reasons I think Microsoft-bashing is counterproductive and probably a poor way to make technical decisions. However, I was very surprised at the number of people who are designing embedded systems today with few resource limitations. In fact, my recent EDN column, a spoof on a 32 bit toaster, elicited a few responses that made me think that perhaps a few such toasters are even now in development!

The quintessential embedded CPU is the 8051, yet there seems a rather significant shift towards much bigger systems. What do you think? I’m collecting info about what people are doing with embedded systems, the sorts of things they are building, and the sorts of processors used. I’d love to hear from y’all about the types of systems you are working on, and will maybe use your input as fodder for a future article.

History of Electronics Article

More Dumb Mistakes

I was testing a prototype of a controller board I had designed. This board had field I/O with LED indicators, microcontroller (6303) and a modem. The LEDs were driven from the digital field inputs via buffers, which could be turned off by software to save power.

While testing the current consumption, I noticed that as I moved my multimeter probe around, the current consumption varied by about 50%! In fact, it wasn't the multimeter - just moving my hands around the board caused the current consumption to vary.

I thought I was looking at some weird capacitive effect, until I noticed that the current drain did not vary when the LEDs were enabled, then the penny dropped. When I turned off the angle-poise lamp above the board, the current consumption dropped to a normal and stable value, and moving my hands around had no effect.

The bright light was causing a photoelectric effect in the LEDs, and the voltage was biasing the reverse-direction buffers in the HCT245s into the linear region, causing the excess current consumption!

The moral of the story - pick one:

Be careful when using components (HC245) for anything other than the purpose for which they were specifically designed,

Don't assume that something that is not enabled can be ignored,

Circuits can sometimes 'think' more laterally than designers :-)

Editor’s note: This is a new one on me. A similar problem comes from not tying off all of the inputs on a CMOS device, so stray pickup creates either linear-biased logic, or (worse) SCR latch-up. The best part of Kris’s email was his sig, which reads: "Good sense is the most valuable good on the market."

Embedded Seminar! Washington DC - Thursday, January 29

The focus is uniquely on embedded systems. I'll talk about ways to link the hardware and software, to identify and stamp out bugs, to manage risk, and to meet impossible deadlines.

Thought for the Week

Every second billions of innocent assembler instructions are
executed all over the world. Inhumanly they are put on a
pipeline and executed with no regard to their feelings. The
illegal instructions are spared, although they should be
executed instead of the legal ones.

Prior to the execution the instructions are transported to a
cache unit using a bus. There they spent their last moments
waiting for the execution. Just before the execution the
instruction is separated into several pieces. The execution
isn't always fast and painless. On crude hardware the
execution of a complex instruction can take as long as 150
clock cycles. Scientists are working on shorter execution
times.

Microsoft endorses the needless execution of instructions
with their products like DOS(TM), Windows(TM), Word(TM) and
Excel(TM). It is more humane to use software which minimizes
the executions.

Modern machines use several units to execute multiple
instructions simultaneously. This way it is possible to
execute several hundred million instructions per second. The
time is near when there will be no more instructions to
execute.

ACT NOW! Before it's too late