Embedded Muse 109 Copyright 2005 TGG January 26, 2005

EDITOR: Jack Ganssle, jack@ganssle.com

CONTENTS:
- Editor’s Notes
- Thought for the Week
- The Digital I/O Handbook
- Embedded Systems Design using the Rabbit 3000 Microprocessor
- Jobs!
- Joke for the Week
- About The Embedded Muse

Editor’s Notes

We’re overwhelmed with jobs this week; let’s hope that says something good about an improved business climate in this industry. In fact, I’m releasing the Muse a bit earlier than planned just so these job offerings don’t go stale.

Thought for the Week

Wow.

Hardware can be made incredibly reliable. But it still breaks. Perfection is not only practically unattainable, the Second Law of Thermodynamics guarantees that no amount of effort will result in perfection. So for the most critical of applications we resort to multiple independent units, and still at best reduce the chance of failure to some non-zero probability.

But software never breaks. It quietly does whatever we told it to do.

It’s not easy to get software perfect, and in fact in many cases that goal may be practically impossible. But there’s nothing implicit in code that leads to bugs. Imperfect software stems from poor programming practices, insane schedules, and all of the usual well-known factors.

Both hardware and software are human creations, so both suffer from human frailties. But only the circuits and devices are intrinsically flawed. If we do better, we can at least approach perfection with the code.

And that’s a happy thought.

The book starts with a quick introduction to logic, which emphasizes the electrical, rather than the Boolean, nature of real devices.

A chapter on outputs is equally practical. The authors talk about using buffer chips and transistor circuits to drive relays (solid state and otherwise) and optoisolators. The chapter on inputs talks about real-world problems like bounce and circuit isolation. You’ll learn how to compute the values of pull-ups, LED resistors, and the like.

The final chapter on interfacing to sensors walks the reader through using thermal switches, Hall-effect sensors, encoders and more.

What I like most about the book is its mix of hardware and software. Most pages have a bit of code plus a schematic. All code snippets are in C.

This is a great introduction to the tough subject of tying a computer to the real world. It’s the sort of quick-start of real value to people with no experience in the field.

I haven’t seen it on Amazon, but you can get it from http://sealevel.com/product_detail.asp?product_id=810&%5F .

Systems Design using the Rabbit 3000 Microprocessor

Rabbit Semiconductor (http://rabbitsemiconductor.com/ ) sells a popular range of 8 bit microprocessors that offer quite high-end performance. My son and I just finished a project for his high school with one, and I’ve used them for a number of other applications. The R3000 is sort of like a Z80 on steroids, with many new instructions, wider address bus and a wealth of on-board peripherals.

Like any modern high-integration CPU the Rabbit offers so much it’s sometimes hard to get a handle on managing all of the I/O. This book will get you started, and is a must-read for developers using the part.

The first few chapters describe the CPU in general and the development environment provided by Rabbit (Dynamic C).

Chapter 5, though, is a description of interfacing to the real world, using all sorts of devices. It’s aimed at engineers, not raw newbies, but, for an engineer at least, is an easy and descriptive read.

The chapter on interrupts is one of the best I’ve seen in any book. It covers the hard stuff, like writing ISRs in C and assembly, with real-world examples. If you’re using the R3000 just cut and paste the code into your application.

It seems today that if there’s a transistor in a product then it needs an Internet connection. Rabbit has several development kits that include everything needed to connect to the ‘net. The authors devote considerable space to networking, but thankfully with only a cursory explanation of protocols. Rather, they give step-by-step instructions on implementing a working network, and conclude with a complete web server for monitoring water sprinklers.

The final chapter covers an alternative toolchain from Softools. Dynamic C is a single-module compile-it-all paradigm that’s highly interactive. Softools (http://www.softools.com/ ) sells a well-supported, reasonably-priced conventional C compiler, assembler and IDE. I only recommend products I’ve used and like, and the Softools products are first-rate.

Systems Design using the Rabbit 3000 Microprocessor is required reading for users of the R3000, and a pretty darn good introduction to the entire realm of embedded systems development as well.

Jobs!

Joke for the Week