Getting ready for the 8800 micro.

Discuss the new Altair 8800 Micro

Getting ready for the 8800 micro.

Postby Kryoclasm » May Mon 25, 2015 12:29 am

I picked up this keyboard off of ebay for use with the 8800 micro.
It is from a model 950 dumb terminal and has a rj-45 connector on the cord. I will either make a rj-45 to ps/2 adapter or just cut the rj-45 off and solder on a ps/2.
I'd rather not cut anything off.

It has a lot ick, dirt and bromide coloration that I will need to clean up.
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Re: Getting ready for the 8800 micro.

Postby Tor6502 » May Mon 25, 2015 2:37 am

What protocol does the keyboard talk? If it doesn't have a ps/2 connector it's unlikely to be ps/2..
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Re: Getting ready for the 8800 micro.

Postby Kryoclasm » May Mon 25, 2015 1:42 pm

it uses standard serial, just a different connector.
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Re: Getting ready for the 8800 micro.

Postby waltermixxx » May Tue 26, 2015 9:00 am

Standard Serial?

PS/2 is not standard serial, it has a clock, data, ground, +5 volts. Standard serial would have something like RX, TX, RTS, DTS and GND that sort of thing... :)
if it is serial and has TX and ground line, then you could use it connected to the serial port assuming the voltage levels match... :) :)

do you have the pinouts for the keyboard? :) not trying to shoot your idea down, just want you to be careful (not knowing your level of electronics...) :)

Cheers and good luck with that... it's a very cool looking keyboard :)
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Re: Getting ready for the 8800 micro.

Postby Kryoclasm » May Tue 26, 2015 3:51 pm

I do have the schematics... I totally forgot about the clock signal.

So, worst case scenario is I will need to make a pic or avr interface to convert the parallel scan codes to a ps/2 format output and provide the clock to it.

Should be doable, I don't see a ready made solution on the Internets. Not a big deal breaker, I just need to do a bit of firmware work and programming.
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Re: Getting ready for the 8800 micro.

Postby waltermixxx » May Tue 26, 2015 5:29 pm

what are the pinouts? what kind of signals are you dealing with? :)
now you have my curiosity peeked :)

Cheers. :)
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Re: Getting ready for the 8800 micro.

Postby Kryoclasm » May Tue 26, 2015 8:19 pm

I found the specs and theory of operation and schematics here:
https://archive.org/stream/bitsavers_televideoMryofOperation26Jan1981_6262088/Model_950_Terminal_Theory_of_Operation_26Jan1981#page/n72/mode/thumb

Lots of good info to reverse engineer this thing. :)
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Re: Getting ready for the 8800 micro.

Postby jac_goudsmit » May Thu 28, 2015 10:47 am

I own a Televideo terminal (mine is a model 925 which is almost the same as a 950 except it uses a lower video resolution and doesn't have smooth scroll). I got it off eBay a couple of years ago because I saw one for sale and I remembered using them when I was studying computer science. They are extremely robust; you have to hit the keys on that keyboard almost as hard as an old mechanical typewriter.

That 950 keyboard looks a bit dingy but can probably be cleaned up very nicely.

You probably don't need extra hardware (besides matching connectors) to connect it to the 8800 if you can modify and reprogram the 8800 CPU. The keyboard has a microcontroller with a 5V TTL serial port, I think it transmits at 1200 or 2400bps but I don't remember (schematics are easy to find). It's probably easy to modify the 8800 firmware so instead of taking PS/2 keyboard signals (data and clock) and translating the scan codes, it just uses the pins for a serial connection and forwards the characters straight to the emulator without translation.

You won't have lights for caps lock and num lock (oh well, big deal). There's also a speaker on board for beeps and key-clicks, but I don't remember if the host (=terminal) has to send serial data to the keyboard to turn the speaker on, or if it's directly connected to the host. Either way, if you're reprogramming the 8800 so that it uses the keyboard data pin as input, you can probably reprogram clock pin as output to control the speaker.

The keyboard normally has a curly cord with a standard RJ11 phone plug (obviously this shouldn't be plugged into a phone jack). The photo doesn't show if the cable is still attached, and I don't know if the keyboard has its own RJ11 jack or the cable is connected on the inside. Either way it should be easy to attach a different cable without damaging it, so that you could return the keyboard to its original state at some point in time.

Interesting factoid: The Televideo 925 and 950 terminals are not as "dumb" as you might think; they're actually a pretty well designed 6502 computers!

===Jac
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