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Taking the Altairs Out for a Ride

ubikuberalles

Entry posted by ubikuberalles

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In early April, a few days before my last two finals, my PC Hardware and Software Administration class had an open lab. By open lab I mean the students were encouraged to bring their own computers to repair or, at the very least, mess around with. I decided to take this opportunity to show my fellow students what computers were like before most of them were born. So I brought a couple of Altairs to the lab.

 

altair04.jpg

 

The bottom one is an Altair 680:

 

altair01.jpg

 

You can program it via the front panel switches or by running the monitor installed in the on-board ROM. To talk to the monitor you connect a terminal to the serial port in the back of the Altair. I have an old ADM-3a "dumb" terminal at home that I use mostly for this but, for the demo at school, I connected the Altair to my old Toshiba laptop:

 

altair03.jpg

 

To talk to the Altair, I used the Kea! terminal emulation program. It works really well and I've used that program to talk to my other computers including my VAXen, Alphas and other Altair computers. One cool feature of the Kea! program is the built-in macro programming language. You can program key sequences in Kea! and you can program it to respond to certain key sequences from the remote host. Thus, I could have whole Altair programs stored on my Toshiba and upload them to the Altair by using a macro program I wrote. It beats to hell the old fashioned method of flipping switches. :)

 

I cut short the demo with the 680 because there appeared to be something wrong with it. Instead of giving me the monitor prompt (the "." character) the computer was repeatedly sending the same character to the terminal. Either a piece of hardware has busted or there is something wrong with the code stored on the EPROM. How long do the bit patterns stay on an EPROM anyway? Twenty years? Thirty years?

 

So, I hooked up the other Altair:

 

altair02.jpg

 

This is the Altair 680b which has the same motherboard as the 680 but has a much simpler front panel. Only two switches instead of the 25 or so on the 680. This means I can only program the 680b through the terminal. However, this computer worked just fine and the "." prompt showed up without much problem.

 

The monitor program for the 680b isn't very sophisticated. It only takes up 256 bytes (that's right, BYTES not Killobytes) of EPROM and it only has a few functions: show memory location, store data to memory, jump to a memory location and other simple functions. I didn't have a program handy to load and so, after showing the basic monitor functions, I shut down the Altair, took off the case and showed off the innards of the machine.

 

altair05.jpg

 

(FYI, I took this and the following pictures later at home).

 

As you can see it's a simple layout. Just a motherboard connected to the front panel and the power supply.

 

Here's a closer look at the mother board:

 

altair06.jpg

 

These computers are capable of expansion. You can see the expansion card slot on the right which follows the S-100 bus format. Just plug a riser card into the motherboard slot and then the expansion card into the riser card and you're good to go. I have a memory card I can install but I have to assemble and test it first.

 

On the right you can also see where the motherboard connects to the front panel.

 

The two chips that power the mother board are seen here:

 

altair07.jpg

 

In the upper right is the 6800 CPU. In the lower left is the 6850 UART used to connect the 680 to the serial line and the terminal. The 6800 uP runs off a 500 KHz clock which means it is only capable of, at most, 250,000 instructins per second (it's been a while but I think the 6800 can execute some instructions in only two clock cycles).

 

This picture shows the memory of the computer:

 

altair08.jpg

 

On the right is where the EPROM resides. Up to four EPROMS can be insalled but currently there is only one in place. That chip holds the on-board monitor program and is, essentially the OS for the machine. As I mentioned before, the ROM monitor is only 256 bytes in size. That fact alone tells you how limited the monitor program is and how tightly the code was packed into the memory.

 

On the left are the main memory chips. Each chip is a 2102 1KX1 static RAM. This gives the machine a total of 1 KB of RAM. Not much room for anything sophisticated which makes the installation of the 16 KB memory board more important.

 

Here's a picure of the power supply for the Altair 680:

 

altair09.jpg

 

Pretty simple, really. It provides 8V and 16V to the motherboard. Components onboard the motherboard regulate the voltage to the 5V necessary to run the chips. The power connects to the motherboard via the white wires. The yellow wires with the red connector connect the motherboard to the RS-232 serial port.

 

So why did I take the 680s instead of the more famous Altair 8800?

 

my-altair.jpg

 

Mainly because they were easier to carry. The 8800 is twice as wide, twice as deep and weighs a lot more than the 680. I was able to carry both 680s and a laptop to class in one trip. If I took an 8800, it would have taken one trip for just one computer. Those 8800s are big and heavy!

 

It small size also means the 680 had much less computing power than it's bigger sister. Here are the stats for the 680:

 

500 KHz CPU clock

1 KB on board memory

256 Byte ROM monitor

On board serial port

Riser card allows up to three expansion cards

 

Compare that with the specs of my 8800a:

 

1 MHz clock

32 KB of memory

Altair Basic stored on 16 KB ROM board

2 serial ports

Motherboard allows up to 8 additional expansion cards (4 slots are currently in use: one for the CPU card, two for the memory and one for the serial I/O board).

 

As you can see the 8800 is much more powerful and a big reason why the 680 series never became as popular as the 8800.

 

Only about a third of the class showed up for the open lab and so I was only able to show it off to a few students. Most of the younger students were unimpressed but a couple of the older students thought it was mildly interesting. One student, who was in his fifties, was interested and started telling me how he used to program compuers with punch cards back in the day (I had to program punch cards for only one semester in college - YUCK! - and I was glad to get it over with). My teacher showed the most interest in the Altairs. When he first started teaching at TVI there were Altair computers in his lab.

 

Even though most of the people there weren't all that interested in the Altair computers, I'm still glad I brought them to school. It was the first time in nearly ten years that I powered those boys up and I'm glad at least one of them was still working (though I thik I can get the other one working pretty quick).

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Serguei2

I always wonder how fun could be have with a computer without a monitor and without a keyboard.

 

Can I play some games with an Altair 8800?

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batari
I always wonder how fun could be have with a computer without a monitor and without a keyboard.

 

Can I play some games with an Altair 8800?

The Altairs have serial ports, so I assume you can at least hook them up to a dumb terminal/teletype and do something other than entering nearly useless programs in binary via the switches, and actually type something in. Or am I overstating the capabilities?

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supercat
The Altairs have serial ports, so I assume you can at least hook them up to a dumb terminal/teletype and do something other than entering nearly useless programs in binary via the switches, and actually type something in. Or am I overstating the capabilities?

 

That's what he said. Though a limit of 1K for everything would still put a severe crimp on things. I've not coded for the 6800, but I understand the 68HC11 is very similar except for the addition of a second index register and a few new instructions. Not sure exactly which HC11 instructions were new, though. One interesting contrast between the 6800 and the 6502 is that the latter uses 16-bit address stored in memory with an 8-bit register displacement; the former uses a 16-bit register address and an 8-bit displacement stored in the code.

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batari
The Altairs have serial ports, so I assume you can at least hook them up to a dumb terminal/teletype and do something other than entering nearly useless programs in binary via the switches, and actually type something in. Or am I overstating the capabilities?

 

That's what he said. Though a limit of 1K for everything would still put a severe crimp on things. I've not coded for the 6800, but I understand the 68HC11 is very similar except for the addition of a second index register and a few new instructions. Not sure exactly which HC11 instructions were new, though. One interesting contrast between the 6800 and the 6502 is that the latter uses 16-bit address stored in memory with an 8-bit register displacement; the former uses a 16-bit register address and an 8-bit displacement stored in the code.

I see that now that I actually read the post...

 

Anyway, terminal games can be fun - it just depends on your perspective. My father took me to work a couple of times when I was really small, I'd say it was '76 or '77 if I had to guess. I played some simple games on a dumb terminal, then printed my name in big letters and a maze on a teletype. I thought it was lots of fun. But then again, our expectations were low back then.

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Serguei2
The Altairs have serial ports, so I assume you can at least hook them up to a dumb terminal/teletype and do something other than entering nearly useless programs in binary via the switches, and actually type something in. Or am I overstating the capabilities?

 

That's what he said. Though a limit of 1K for everything would still put a severe crimp on things. I've not coded for the 6800, but I understand the 68HC11 is very similar except for the addition of a second index register and a few new instructions. Not sure exactly which HC11 instructions were new, though. One interesting contrast between the 6800 and the 6502 is that the latter uses 16-bit address stored in memory with an 8-bit register displacement; the former uses a 16-bit register address and an 8-bit displacement stored in the code.

I see that now that I actually read the post...

 

Anyway, terminal games can be fun - it just depends on your perspective. My father took me to work a couple of times when I was really small, I'd say it was '76 or '77 if I had to guess. I played some simple games on a dumb terminal, then printed my name in big letters and a maze on a teletype. I thought it was lots of fun. But then again, our expectations were low back then.

 

Thanks for the explanations.

 

I thought the altair could be used alone but it needs a terminal to get it to work. I was not sure what I read about this topic.

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batari
Thanks for the explanations.

 

I thought the altair could be used alone but it needs a terminal to get it to work. I was not sure what I read about this topic.

I think the 8800 can be used without a terminal, but it's not particularly easy. I heard a story of a guy who made his the Altair play the song "Daisy" on a nearby AM radio, and I hear he programmed it using just the switches. I guess the Altairs weren't FCC compliant?

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EricBall
I always wonder how fun could be have with a computer without a monitor and without a keyboard. Can I play some games with an Altair 8800?

Well, I once had a book of programs for the KIM-1, which was a 6502 based computer with a only hex keypad and a LED display. The book gave a bunch of games, including classics like "hunt the wumpus". I suspect you could even adapt some of them to be playable with only lights and switches. You just have to know what each input & output means then use your imagination.

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Serguei2
I always wonder how fun could be have with a computer without a monitor and without a keyboard. Can I play some games with an Altair 8800?

I suspect you could even adapt some of them to be playable with only lights and switches. You just have to know what each input & output means then use your imagination.

 

 

I could difficult to play games with only switches and leds and use my imagination to play them,

 

Thanks to Apple Computer to released Apple 1, the first computer using with a monitor (or TV) and keyboard, or our computers are still have switches and leds.

 

I found more things about Altair 8800 in wikipedia.

 

http://en.wikipedia.org/wiki/Altair_8800

 

So an Altair could be upgrated to 4k, added a monitor and a keyboard. Amazing.

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ubikuberalles

Wow. I'm surprised and quite pleased in the response. I didn't think too many people would be interested in these old computers (based on my experience at school, anyway).

 

Let me answer some of the comments and questions posted here. I'm not a bon-fide Altair historian but I'll answer based on my experience.

 

I always wonder how fun could be have with a computer without a monitor and without a keyboard.

 

How much fun can you have with a computer without a monitor and a keyboard? Not much. However, in those days, people were deperate to get their hands on a working computer. Back then the choice was either a computer without a keyboard and monitor or nothing. Most chose the former. The front panel for the 8800 works also as an I/O port: you can set the LEDs to display a pattern and you can sense which switches the user flips. I remember reading the description of one game with the name something like: "Catch the LED". The front panel would display a moving light and you were to try to catch the light by flipping the switch at the same location the lit LED was supposed to be. It only took up 256 bytes and so most newbie Altair owenrs were able to program that game.

 

There were also a whole bunch of number guessing games you can play using only the front panel. Boring stuff but remember most people got the computer just so they an learn about computers and brag to their neighbors that they actually own a computer.

 

Can I play some games with an Altair 8800?
Sure, and pretty good games if the computer is equipped properly. By properly equipped, I mean the computer had to have at least 16K of RAM, a serial I/O card, a cassette interface, a terminal and MITS 8K Basic (it was called 8K Basic because it would only work if you had at least 8K of memory on your computer). My favortie game on the Altair was Star Trek. You might have been familiar with the game as there have been several similar versions written for the Atari 8 bit and the Atari ST (in fact there was a version called Star Fleet I for the Atari ST published by Interstel).

 

Most of the games I programmed into my dad's Altair came from the book 101 Basic Computer Games Edited by David M. Ahl. Many came from the various magazines published at the time including Byte magazine. The version of Star Trek I entered into the Altair came from the magazine "Interface Age" which was the official magazine of the Southern Calif. Computer Club.

 

If it wasn't for these fun games for the Altair, I'm sure my interest in computers would have waned quickly (until, that is, the Atari 400 came out :D ).

 

I am not familair with what games were written for the Altair 680 computers. Not many, I'm sure, since it was not a very popular computer.

 

If I am energetic enough, I may program a number guessing game on the Altair 680. The first barrier to overcome is to find an algorithm for a psuedo-number generator I can program in 6800 machine code. I'll post an entry in my blog if I have any results.

 

Just like playing BBS games in the 80s :)

 

That's pretty true! ;) I remember, when I first got on a BBS, that the games were a lot like that on my dad's Altair. The difference, of course, is the BBS versions allowed multiple players.

 

I think the 8800 can be used without a terminal, but it's not particularly easy. I heard a story of a guy who made his the Altair play the song "Daisy" on a nearby AM radio, and I hear he programmed it using just the switches.

 

I remember hearing that story nearly thirty years ago. The Altairs generated a low level of radio noise that you could pick up by tuning your AM radio to the bands between radio stations (where you would normally hear static). A song could be made by having the Altair go into a series of loops. No hardware mods were necessary for this program to work which is what made it so unique. Later programs either required a sound card or at least a parallel port hooked up to a speaker.

 

I guess the Altairs weren't FCC compliant?

 

No and they weren't required to be FCC compliant. I think the FCC didn't get involved until people (Like Atari) put RF modulators on their computers so you could hook them up to your TV.

 

Without a doubt the Altairs were noisy, R/F wise. In my early college days I rented a room at a house and I had borrowed my dad's computer. I had to curtail my evening programming because the landlord was complaining about the computer interfering with the TV! It had produced wavy lines on the screen and I could only run the computer in the mornings and afternoons when my landlord was at work.

 

I've been asked to bring my Altair 8800's to OKVE and I plan to do that. So stay tuned for more Altair posts once I work on them some more and have something to report.

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supercat
it was called 8K Basic because it would only work if you had at least 8K of memory on your computer

 

Was the BASIC in ROM/EPROM, or did you have to get it into RAM? I think ROM was cheaper than RAM in those days, so I'd think the former, but that would leave the question of why a BASIC interpreter would require 8K of RAM. The Sinclair ZX-80 survived with 1K, and Warren Robinett's BASIC interpreter only needed 128 bytes.

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ubikuberalles
Was the BASIC in ROM/EPROM, or did you have to get it into RAM? I think ROM was cheaper than RAM in those days, so I'd think the former, but that would leave the question of why a BASIC interpreter would require 8K of RAM. The Sinclair ZX-80 survived with 1K, and Warren Robinett's BASIC interpreter only needed 128 bytes.

 

Only one version of Altair BASIC resided in ROM. The rest resided in RAM.

 

Here are the versions, as I remember them:

 

4K BASIC

8K BASIC

Extended BASIC

Extended ROM BASIC

Disk BASIC

 

4K, 8K and Extended BASIC were availabe on cassette tape while Extended ROM BASIC was installed on a ROM card and Disk BASIC came on floppy.

 

A couple years after we got the Altair, my dad bought a floppy drive for the system. It was a North Star 5 1/2" floppy drive (instead of the Altair 8" floppy - the North Star drive was much cheaper) and my brother figured out how to save the 8K BASIC image to disk. This was a great savings in time because, before we got the floppy, it took at least ten minutes to load BASIC by cassette plus five or ten minutes to load the bootstrap program via the front panel switches.

 

Today my Altairs run on Extended ROM BASIC. It's a good thing too as the North Star disk drive isn't working right now.

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