Pre 1980 Micro-Computers

Here are some of the early systems (pre 1980) that “Got me interested..” prior to buying my first computer. (Radio Shack TRS-80 Model 1)

KIM-1

MOS Technology's first processor, the 6501, could be plugged into existing motherboards that used the Motorola 6800, allowing potential users (i.e. engineers and hobbyists) to get a development system up and running very easily using existing hardware. This enraged Motorola, who immediately sued, forcing MOS to pull the 6501 from the market. Changing the pin layout produced the "lawsuit-friendly" 6502. Otherwise identical to the 6501, it nevertheless had the disadvantage of having no machine in which new users could quickly start playing with the CPU. Chuck Peddle, leader of the 650x group at MOS (and former member of Motorola's 6800 team), designed the KIM-1 in order to fill this need. The KIM-1 came to market in 1976. While the machine was originally intended to be used by engineers, it quickly found a large audience with hobbyists. A complete system could be constructed for under 500 US$ with the purchase of the kit for only 245 US$, and then adding a used terminal and a cassette tape drive.
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Many books were available demonstrating small assembly language programs for the KIM, including “The First Book of KIM” by the legendary Jim Butterfield et al.

One demo program converted the KIM into a music box by toggling a software-controllable output bit connected to a small loudspeaker.

As the system became more popular one of the common additions was the Tiny BASIC programming language. This required an easy memory expansion; “all of the decoding for the first 4 K is provided right on the KIM board. All you need to provide is 4 K more of RAM chips and some buffers.” The hard part was loading the BASIC from cassette tape – a 15 minute ordeal.

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Altair 8800

The MITS Altair 8800 was a microcomputer design from 1975 based on the Intel 8080 CPU and sold by mail order through advertisements in Popular Electronics, Radio-Electronics and other hobbyist magazines. The designers hoped to sell only a few hundred build-it-yourself kits to hobbyists, and were surprised when they sold thousands in the first month. The Altair also appealed to individuals and businesses who just wanted a computer and purchased the assembled version. Today the Altair is widely recognized as the spark that led to the microcomputer revolution of the next few years: The computer bus designed for the Altair was to become a de facto standard in the form of the S-100 bus, and the first programming language for the machine was Microsoft's founding product, Altair BASIC.
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MEK6800D2


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The MEK6800D2 was a development board for the Motorola 6800 microprocessor, produced by Motorola in 1976. It featured a keyboard with hexadecimal keys and a LED display, but also featured an RS-232 asynchronous serial interface for a Teletype or other terminal. There was an on-board debug program called JBUG fitted in a 1k ROM, and the maximum RAM capacity on board was 512 bytes, but this could be expanded via the Motorola EXORciser computer bus interface. There was also a parallel bus interface for general purpose I/O. Another popular monitor program for this system is called MIKBUG.

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Mini-Scamp


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The Mini-Scamp was based on the SC/MP CPU from National Semiconductors. It boasted a massive 256 bytes of RAM - this was 4 times more than the earlier model. It had no ROM or EEPROM of any kind. The complete user interface consisted of 18 toggle switches, 2 pushbuttons and 9 LEDs. Binary code was entered into the RAM by dialing up the data byte and address in binary using toggle switches.

Pressing the deposit button stored the byte in memory. The LEDs showed the current contents of the memory location. After the program was entered in this manner one of the switches on the right was flipped from DMA to run mode and the code was executed. The micro could display bytes on the LEDs and read bytes from the data switches - the request LED was there to signal the user to enter a byte and press deposit.

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Altair 680


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The diminutive Altair 680 was one of the first three Motorola 6800 computers on the market, along with the SWTPC 6800 and Sphere. Although the 680 was "pre-announced" on the cover of the November, 1975 issue of Popular Electronics (following the similar introduction of its big brother, the Altair 8800), the headline trumpeting "THE FIRST MOTOROLA 6800 COMPUTER PROJECT" was not the whole truth. Ironically, page 5 of the same magazine carried an ad for the Sphere, a 6800 based computer available in kit form for $860, and page 89 advertised the SWTPC 6800 kit at $450. It's hard to say which computer actually shipped first in quantity.

MITS offered a discount for orders placed before December 31, 1975, but the ads offering the discount featured a picture of the mockup 680 that appeared on the Popular Electronics cover (yes, the 680 was a mockup, just like the 8800 photo on the magazine cover the previous January). Also, the "December 31, 1975" discount ads appeared in Byte magazine as late as February 1976. The 680 is much smaller than the 8800, measuring only 11" by 11" by 4-3/4".

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DREAM 6800

Dream 6800 was a “kit” computer. The design was originally published in ELECTRONICS Australia, May, 1979 starting on Page 83.

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Talks directly to your TV and is programmed in a high-level language!

Are you one of the many people who have been turned off microprocessors and computers by all the complexity and never-ending jargon? Well, here is your chance to really start learning about the subject. This simple and easy to build computer costs around the $100 mark, yet talks directly to your TV without the need for a costly video terminal.

One of the other big features is the built-in cassette interface which means you can store your programs on any cassette recorder. And there isa whole raft of sample programs to get you started. All you have to do is punch them in via the hexidecimal keyboard. In no time you'll have the whole library of your own programs, easily accessable on cassettes.

So start reading now. We've even provided a comprehensive glossary to help you wade through all the jargon which is inevitable in this new and exciting field. The title of the computer is itself a bit of jargon: Dream 6800, which stands for "Domestic Recreational and Educational Adaptive Microcomputer.."

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Now we’ll let the designer, Michael Bauer, of the Division of Computing and Mathematics at Deakin University, tell his story…

Surprising as it may seem, there are very few co-called “hobby computers” which inexpensively satisfy the needs of recreational home computing. The choice is between an “evaluation kit” (eg, 6800-D2, KIM-1, Mini-Scamp etc) or a BASIC system with a CRT terminal, 8k memeory, etc. The latter will set you back a few hundred dollars, while the evaluation kit doesn’t give you enough capabilities. And besides, a hobby is supposed to be pleasurable, not give you headaches. There are much easier and less expensive ways to produce a headache, other than sitting up all night for days on end, hand assembling a ridiculous machine-code program to play “Lunar Lander” (with a 7-segment LED readout), or trying to write an animated video game in a high-level language like BASIC which wasn’t invented for that purpose in the first place for a terminal that only displays alphanumerics.

Here’s what the “Dream 6800” home video computer has to offer:-

  • Lower Cost: the parts should come to about $100
  • A more useful display: Chunky graphics output to your colour or B&W TV giving a 64 x 32 dot matrix display.
  • Better Software: As well as the usual operating-system or monitor (used for memory examine and deposit, tape load and dump, go to user program, etc), CHIPOS incorporates a high-level language interpreter, CHIP-8, which was specifially invented for video games, graphic displays, simulations, etc. Further, CHIPOS supports machine-language programs as well, for the applications where CHIP-8 is inadequate.
  • Wider Appeal: People not into electronics or computing will also find the Dream 6800 fascinating. Lots of TV games and other programs have already been written in CHIP-8, so you’ll be able to impress your “non-believer” friends right away. And you wont hear the old: “Oh yeah, but what does it do?” and similar phrases. This is a fun computer!
  • There are hundreds of applications: TV games; advertising displays; teaching young children elementary arithmetic; practising morse code; timing events in the kitchen; hex/binary (variable base) calculator; metric conversions; bar charts; simulations (like LIFE); data communications experiments; etc.

Educational institutions will find it highly motivational for introductory machine-level programming courses. It’s also a serious computer!

Hardware Specifications

  • Processor: Motorola M6800.
  • Clock: M6875 with 4.00 Mhz crystal.
  • RAM (On-card): 1K x 8 (2 x 2114) Off-card expansion to 32K.
  • ROM (CHIPOS) 1K x 8 (2708).
  • Display: 64 x 32 dot matrix; each dot is 4 TV lines square. Uses 256 bytes of RAM at loc. 0100 for refresh by DMA. Video output: 1Vpp @ 75 ohm.
  • Input/Output: One M6821 PIA controls:
    • Hex keypad (16 keys, Function and Reset.
    • Tape I/O: 300 Baud; 2400/1200Hz FSK; Out: 0.5Vpp; In: 300mV - 3Vpp.
    • RTC timer interupt: 50Hz (frame sync).
    • Audio Bleeper: 2400/1200Hz (8 ohm spkr).
    • Display/DMA enable-disable line.
    • Add extra PIA’s, ACIA’s, etc, without any additional logic.
    • Power requirements (worse case): +5V (1A), -5V (100mA), +12V (100mA).

Note: Power supply, keypad and TV RF modulator are off card extras.

Right about now the sceptics will be saying: “But there is only 1K of RAM and the video refresh buffer’s got to be in there somewhere, and a scratchpad, and a stack or two… good grief! there won’t be enough left for a program! In fact there are 640 bytes free. Thats either a damned long machine-code program to hand-assemble, or a 320 statement CHIP-8 program. Most users will find this more than adaquate. CHIP-8 is a lot more memory-efficient than BASIC, assuming the application is graphics orientated and does not require any heavy number-crunching, or text manipulations.

For experimenters, there are a few spare I/O lines on the PIA and the system bus in terminated on two 16-pin sockets allowing memory and I/O expansion.

Most hobby computer designers take advantage of the increase in sophistication and lower cost of hardware to produce a more powerful system for the same price as earlier designs. The DREAM-6800 philosophy is to retain the meek processor power and small memory size of past generations, but at a much reduced cost, and to more effectively utilise the available memory. This is not to imply that the ‘6800 lacks power’; it is a superlative 8-bit MPU in every respect.

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