Re: [midatlanticretro] Altair 680 Project Update
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:
> I re-read your pages and the manuals I have. Frankly it's confusing.
> Here is how I interpret what I have read:
> ...seems to indicate that only If I am using a baudout TT I need the
> chip in the L slot, otherwise no IC is needed in IC L.
> ...but then...
> Take a look at page 17 of 37:
> How do you interpret this? This is my source for why I think that the
> 74L123 is needed in slot L.
> 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,
> that it works! Schematics confuse me.
> How does your motherboard I/O circuitry compare with mine?
> Thanks very much.
> 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.
> >[ My Corner of Cyberspace http://ragooman.home.comcast.net/
> <http://ragooman.home.comcast.net/> ]
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