Briel Computers Altair 8800 micro User manual

Altair 8800micro
Setup and Users Manual
Setup and Users ManualSetup and Users Manual
Setup and Users Manual
JULY 2010 PRELIMINARY MANUAL
Briel Computers
Briel ComputersBriel Computers
Briel Computers
5392 Cornell Blvd
North Ridgeville, OH 44039

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All materials, schematics, and hardware designs provided without any warranties. Although this material has been carefully examined,
Briel Computers takes no responsibility for any errors in printing.
Version 1.0
Published by Briel Computers
5392 Cornell Blvd
North Ridgeville, OH 44039
USA
Copyright 2010 Briel Computers; All rights reserved. Printed in the United States of America. Except as permitted under the
Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a
database or retrieval system, without the prior written permission of the publisher, with the exception that the program listings may be
entered, stored, and executed in a computer system, but they may not be reproduced for publication.

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Forward
ForwardForward
Forward
Recreating a cult classic
Anybody who has been even remotely involved in vintage computers knows of the Altair 8800. There have
been many discussions on the first personal computer, the first home computer, but nobody can argue that the
Altair set the industry in motion.
Original Altair 8800 system
The original Altair 8800 was designed in 1975 by Ed Roberts founder of MITS (Micro Instrumentation and
Telemetry Systems).
Ed Roberts shown next to some of his Altair machines

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In 1977, Ed Roberts moved back to rural Georgia after the sale of MITS to Pertec. Nearby Mercer University
started a medical school in 1982 and Ed Roberts went on to be the first graduating class and get his medical
degree in 1986. He did his residency in internal medicine and in 1988 established his own practice. Ed Roberts
died on April 1, 2010 after a long bout of pneumonia at the age of 68. The computer system he created was
introduced to the world in the January 1975 edition of Popular Electronics and shall live on forever.
January 1975 Popular Electronics featuring the ALTAIR 8800
The article describes the entire system of the Altair and took two issues to cover the entire system. The
production version was not ready at the time and MITS had this case made for the magazine article. You could
purchase an affordable base kit for $439 which included the case, CPU board and 256 bytes of memory. The
assembled version was $621. Soon after the release Bill Gates sent Ed Roberts a letter stating he had a software
company that had BASIC that would work on the Altair. Paul Allen came to MITS in Albuquerque to
demonstrate their program using paper tape; it crashed after it displayed “Altair Basic”. The next day a new
paper tape reader was brought in and BASIC loaded successfully. This was the beginning of Microsoft, the
largest software company in history.
Copies of BASIC were bundled with a pair of Altair 4K RAM boards for $75. However, the RAM boards were
flawed and most users did not want those boards. Robert Marsh who formed Processor Technology offered 4K
static RAM boards for $255. His company was the most successful company that produced Altair compatible
products. This kept many hobbyists from wanting the flawed 4K MITS boards and the full retail price for
BASIC from Micro-Soft was $500. The Homebrew computer club was formed in 1975 and the primary
computer there was the Altair 8800 system. Steve Dompier passed a copy of the pre-release version of BASIC
to Dan Sokol who had access to a high speed tape punch. The next day at the Homebrew Computer Club
meeting, 50 copies of BASIC were made available to members for $.50 each. Shortly, many people had copies
of BASIC and were passing it along freely. Word of this got back to Bill Gates and prompted this open letter to
hobbyists in 1976:

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The second letter was sent out to all major computer publications after a very strong negative response from
many in the field.
In late 1975 Imsai released the 8080 as a direct competing clone of the Altair. Most feel that the Imsai was a
better machine than the Altair and used the same bus expansion scheme. It wasn’t long before several other
companies also had clones using the S100 bus system. This led to several aftermarket companies developing
hardware add-on cards for the S100 bus systems.
By 1977 MITS had reached $6 million in sales when they were sold to Pertec. The company was soon merged
into the larger company (Pertec) and the name abandoned. The S100 bus system computers continued to be sold
well into the mid 80’s and I remember as late as 1990 still seeing ads for S100 boards in magazines.
The Altair 8800 is an icon for the start of the home computing industry. Long live the blinking lights :.::.:
Vince Briel

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Setup and Users Manual
Index
Chapter 1: Introducing the Altair 8800 micro 9
Chapter 2: Unpacking your system 13
Chapter 3: Building your kit with step by step instructions 15
Chapter 4: Powering up and testing your system 23
Chapter 5: Programming with the front panel 27
Chapter 6: Loading BASIC 29
Chapter 7: Saving memory to an SD card 30
Chapter 8: Loading a text file BASIC program listing 31
Chapter 9: On screen graphics and color 32
Chapter 10: Special front panel functions 33
Chapter 11: Performing a firmware update 35
Appendix A: Troubleshooting 36
Appendix B: The expansion port 37
Appendix C: Bill of materials 38
Appendix D: VT100 Control Commands 39

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Chapter 1: Introducing the Altair 8800 micro
The Altair 8800 micro is the result of 5 years of concept ideas and many failures. While the project spent much
time on the shelf, the desired result would keep this project alive. The micro is based on a simple early version
Altair 8800 with memory and a serial card for I/O. The project goal was to design a system that could be
programmed like the original with toggle switches and could run the original Altair BASIC programming
language. The micro is the first in a series of Altair clones that will be released. A full size version will be in the
works after the initial release of the micro that will be a front panel only and then the original concept AltairPC.
Final Altair 8800 micro prototype
You may have noticed that not all of the original Altair I/O status LED’s are on the front panel. This is due to
the limited amount of I/O and the limited amount of physical space allotted on the front panel itself. The
missing LED’s are INTE, PROT, WAIT, and HLDA. In addition to the missing LED’s one AUX switch was
also not included on the board. The AUX switches were not directly used on the original Altair but the one
AUX switch on the Altair micro serves as a boot loader and memory storage detector.
Choosing a processor was no easy choice. Most replica computers created by Briel Computers use authentic
processors that are identical to those used in the original systems. The Altair 8800 micro is different. The
original processor (i8080) has multiple voltage requirements making design implementation difficult for kit
purposes at a low price. The Z80 processor is very close to the 8080 and most code works with it. The problem
is that it doesn’t run Altair BASIC and was one of the failed concepts. This processor failure set the project
back over 2 years. After considering using the 8085 (software compatible), I opted to emulate the CPU in a
microcontroller. The main reason was chip reduction. With a microcontroller I am able to not only embed an
emulated version of the 8080; I can also emulate most of the Altair system in 1 chip. The main CPU
microcontroller has the nickname AOAC (Altair on a chip). While there are I/O pin limitations, a handful of
latches can give you as much I/O as you need.

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Writing an emulator for a CPU is a very difficult process if you’ve never written an emulator and you have very
little programming experience on the CPU you are emulating. My first step was to learn about a CPU that I
hadn’t used in 20 years. Many CPU’s share similar features such as accessing memory, having registers to work
with, math functions, ability to call routines, jump to memory locations, etc. It wasn’t long before I had a good
handle on the CPU and how it functioned. The hardware is a simple design. Using the Atmel AVR family
microcontroller was a simple choice. It is RISC based and many of the instructions only require one clock cycle
to perform. The heart of the code simply reads a memory location OP instruction and handles that instruction
exactly like the 8080 would. Some instructions were almost directly compatible to the Atmel instruction set
making emulation easy. Other instructions were much more difficult and required more code to interpret the
command.
Single step introduced a whole other problem. Not only does the microcontroller emulate the instruction, it
breaks it down into steps. As the original Altair single-steps through code, it does so one section of the
instruction at a time. For example, a jump to another address command first gets the opcode, and then on the
next step it fetches the low order byte of the address it is going to jump to. On the final step, it grabs the high
order byte. The next step will place the CPU at the new address.
With the core of the CPU and front panel emulation complete, the built on terminal section received its features.
The terminal section is from the Briel Computers PockeTerm with a lot of changes. The addition of an SD card
slot gives the ability to load and store programs and memory.
SD card slot on Altair 8800 micro
The SD card has the following features and conditions:
•Cards work with FAT16 or FAT32 only, no NTSF
•8.3 filename format, no using long names
•Root directory access only, no reading/writing to subdirectories
•Micro-SD cards can be used with an adapter
•Cards must not be removed while the system is on
The purpose of the SD card is to store and load BASIC, complete memory including BASIC and firmware
updates. The card was not designed to load disk operating systems and other such means of storage.
Modifications may be possible to do this in the future but not at this time.