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Re: [midatlanticretro] Altair 680 Project Update

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  • B. Degnan
    Good and bad then...I don t need the chip, but now I don t know why the system is not communicating to the terminal. I will return to my original plan, to put
    Message 1 of 48 , Mar 3, 2007
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      Good and bad then...I don't need the chip, but now I don't know why the
      system is not communicating to the terminal. I will return to my original
      plan, to put a scope to the system to try to find what's happens when I
      engage the monitor program (@ FF02). I have what appears to be a working
      monitor prom, at least the memory checks out with the prom code to the best
      of my knowledge.

      I know that Herb Johnson has some ADM terminals for sale, or at least he
      did last year..
      Bill

      At 02:38 PM 3/3/2007 -0500, you wrote:
      >Bill,
      >
      >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
      >match.
      >
      >=Dan
      >
      >[ 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/> ]
      > >
      > >
      > > ------------------------------------------------------------------------
      > >
      > > No virus found in this incoming message.
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      > > Version: 7.5.446 / Virus Database: 268.18.6/708 - Release Date:
      > 3/2/2007 4:19 PM
      > >
      >
      >
      >
      >
      >Yahoo! Groups Links
      >
      >
      >
    • Evan Koblentz
      DG Eclipse S/140 from a couple of months ago, now on display in our museum, next to Perkin-Elmer 3120.
      Message 48 of 48 , Mar 20, 2011
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        DG Eclipse S/140 from a couple of months ago, now on display in our museum, next to Perkin-Elmer 3120.
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