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5057Re: [midatlanticretro] Altair 680 Project Update

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  • Dan
    Mar 3, 2007

      That schematic is for the front panel on the 680b, they called it the
      "Display" panel, sheet 4/4 of the schematics. All the LD1 to LD 27
      diodes are actually the LEDs on there--LD for _L_ight emitting _D_iode--

      So for the 680b model, IC L is not needed for RS232, you can see on that
      schematic I scanned that the 6850 ACIA pins TX and RX are connected to
      the RS232 Level converter circuit using IC A, Q200, D200 and a few
      resistors. While the Baudot interface with IC L acutally bit bangs the
      baudot code out the connector.

      Also on the 680b--in the Assy manual--, the ACIA monitor fits in socket
      IC T while the other option back then was to order the 2 Baudot monitor
      Eproms which fit in sockets IC T and U. You said that your ordered the
      ACIA monitor eprom, right ?

      MITS obviously went through a big rev change to make the 680b. I've
      never had seen the Altair 680 up close, just the 680b.

      If they dont have the 680b schematics on there, I can scan mine this
      weekend. I can also scan the assembly doc --it'll take a while--which
      shows how to configure all the jumpers and components options--you'll
      have to excuse my notes that I scribbled on there--

      Funny you should ask about the I/O on mine, it's still wired for an ASR
      :) since we had access to a teletype back then. Mine works, but I'm only
      using the front panel right now. I'm in the middle of restoring the chip
      sockets 'cause they're getting old and flakey. Once I do that, I was
      going to switch it to RS232 and use my PC to get BASIC running on this too.

      If I'm lucky I can find a ADM terminal real cheap to sit beside this. I
      have my H9 terminal which belongs to my Heathkit H8, but it just doesn't


      [ My Corner of Cyberspace http://ragooman.home.comcast.net/ ]

      B. Degnan wrote:
      > Dan,
      > I re-read your pages and the manuals I have. Frankly it's confusing.
      > Here is how I interpret what I have read:
      > http://ragooman.home.comcast.net/files/vintage/altair/assypg16sm.pdf
      > <http://ragooman.home.comcast.net/files/vintage/altair/assypg16sm.pdf>
      > ...seems to indicate that only If I am using a baudout TT I need the
      > 74LS74
      > chip in the L slot, otherwise no IC is needed in IC L.
      > ...but then...
      > Take a look at page 17 of 37:
      > http://www.vintagecomputer.net/MITS/680/MITS_Altair_680b_Theory_of_Operation_Manual.pdf
      > <http://www.vintagecomputer.net/MITS/680/MITS_Altair_680b_Theory_of_Operation_Manual.pdf>
      > How do you interpret this? This is my source for why I think that the
      > 74L123 is needed in slot L.
      > Questions:
      > 1) Do I need *any* chip in the L slot?
      > 2) Do you have a working system that uses a terminal? If you have a
      > working system than I would like to try to match your configuration,
      > being
      > that it works! Schematics confuse me.
      > How does your motherboard I/O circuitry compare with mine?
      > http://vintagecomputer.net/MITS/680/pictures.html
      > <http://vintagecomputer.net/MITS/680/pictures.html>
      > Thanks very much.
      > Bill
      > At 06:36 PM 3/2/2007 -0500, you wrote:
      > >Well, it seems very odd that with the same rev1-6X motherboard that MITS
      > >would use two different IC's. I checked your pics of the motherboard and
      > >its the same as mine. I also have the round toggle switches on mine.
      > >Have you check the Assembly doc PDF's I posted online to compare ?
      > >
      > >All I remember is that the 680 had a front panel with a different color,
      > >aside from a different rev motherboard too I suppose. I recall seeing a
      > >pic online somewhere but I don't seem to have that bookmark.
      > >
      > >I posted sheet 2(rt.half) from my schematics showing IC L being a
      > >74LS74, the pinouts checkout accordingly.
      > >http://ragooman.home.comcast.net/computers_altair680.html
      > <http://ragooman.home.comcast.net/computers_altair680.html>
      > >
      > >=Dan
      > >
      > >[ My Corner of Cyberspace http://ragooman.home.comcast.net/
      > <http://ragooman.home.comcast.net/> ]
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