|
Hi
Josh and John -
Well,
I think I confused things by describing two different issues in the same
email.
The
first issue was regarding a SSM-IO4 card I picked up recently. It has bad
DIP switches, probably corroded from improper storage for many years. But
the board works, once you pick an address that is compatible with the corroded
DIP switches. At least, so far. I've tested output to one parallel
port and one serial port.
The
second issue is with boards that were part of the original Altair box which has
been properly stored. When running a memory test on my 1K card it will
randomly and very occasionally (every 2-20 hours) spontaneously go into memory
protect mode, and even more rarely, drop a bit. It is this symptom
that has me thinking there might be a bus noise issue, especially as
those old Altair busses appear to be famous for that. This
actually seems consistent with John's statement that:
" At low speeds like 2-4MHz you will
occasionally have a system randomly hang from bus
noise"
So I'm
still thinking that a terminator is a good idea, at least if I would like the
system to not hang occasionally. I figure I can try it and if it doesn't
help, I can eliminate that nagging doubt. I really have no other idea what
could be going on with something so sporadic.
In any
case, I appreciate all the good advice I'm getting here, so
thanks!
-
Eric
PS: I
have a good soldering iron. For desoldering I use a vacuum bulb
desoldering iron. There's usually so little solder left that the pins can
be broken free with a bit of effort, but it isn't a quick
process. Of course, if you're OK sacrificing the chip, then cutting off
the leads and desoldering them one by one is the way to go. I'd like to
get a vacuum pump desoldering station, but a good one is pretty expensive.
What I've seen on ebay has been either very expensive or in really bad
shape.
Hi John, Eric, I think John's right. The dipswitch had
too much oxidation on the contacts, so it's probably a system wide
problem. My Ohio Scientific Superboard had the same problem, I replaced at
least 1/2 the sockets before it started working. Looking back, now I wish I
had changed them all, because when the others fail, I may not know which sockets
are done already. I hope you have a decent temperature controlled
soldering iron and a good solder sucker. I always recommend the Soldapult
DS-017, full length. It would be even better if you had a full desoldering
station, I picked up a 2nd hand PACE unit with a hollow tip and vacuum for
cheap. A solder pot is probably the fastest, I wish I had one of
them. Cheers, Josh
From: mon...@vitasoft.org To: n8vem...@googlegroups.com Subject: RE:
[N8VEM-S100:1506] New/Old Project (Altair restoration) Date: Mon, 11 Mar 2013
16:45:05 -0700
FWIW,
I don?t think bus noise is your problem. At low speeds like 2-4MHz
you will occasionally have a system randomly hang from bus noise, but if you
have consistent problem it?s usually a connection, socket a bad IC or an
incorrect jumper/setting. At these kind of speeds, 74XX or 74LSxx are
fine.
From:
n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com] On Behalf Of
Eric Osman
Sent: Monday, March 11, 2013 4:23 PM
To:
n8vem...@googlegroups.com
Subject: RE: [N8VEM-S100:1505] New/Old
Project (Altair restoration)
Hey,
thanks for all the useful code! I'm a little closer to being able to make
use of it. I've been working on the SSM-IO4 card and can now output to
parallel port A. The DIP switch for the parallel port address is
not working correctly. 5 of 7 switches don't make contact when
"closed". It took me a while to figure that one out. Who would have
thought that those switches would go bad? But, I guess they have contacts
inside that are subject to corrosion. Probably, the board wasn't stored
properly at some point. There are other signs of poor storage, as well,
such as dirt.
Regarding
my CPU card, I read somewhere of someone who used a function generator to slow
down an Altair CPU, but I think I'll wait a bit before trying that. Right
now, I think my biggest issue is bus noise, so I'm going to try the N8VEM S-100
Terminator/prototype card when it comes.
I've
been reading through an extended discussion of bus issues on the retrotechnology
web site:
The most
important point to me is this:
"Lee Hart:
However, I'm not sure
that propagation delays are the issue for bus noise. What I see happening is
that the S-100 bus was designed for old slow TTL, and isn't suited for modern
high-speed logic. If you just substitute faster chips (74LS --> 74S -->
74ABT etc.), the speed of the rising and falling edges are so sharp that they
generate lots more ringing and noise. And, the faster chips are capable of
*responding* to this noise as if it were signals. "
When I
replaced the chips on the CPU and front panel, I used almost all LS or ALS
parts, usually in place of regular old 74xx chips, and I suspect that these
faster chips are causing additional bus noise. In the above discussion,
Lee goes on to suggest 74HC types as they have softer rise/fall
times.
There is
also a discussion of how the worst ever was the Altair bus with two 4
slot backplanes wired together, plus a bunch of long wires going to the
front panel. Guess what? That's exactly what I have. But I'd
prefer to keep it that way if possible, for the sake of keeping the system as
"original" as practical. I do have another mobo I can put in there if
worse comes to worse.
HI
Eric,
It's only 16 bytes so it's very simple.
;16 BYTE BOOT STRAP TO LOAD PROGRAM FROM
SERIAL PORT.
0000 211000 LXI
HL,$0010 ;First free location
0003
DB00 IN 00 ;GET UART
STATUS
0005 07 RLC
;SHIFT DAV TO CARRY FLAG
0006 DA0300 JC
$0003 ;LOOP BACK UNTIL RXCHAR
0009 DB01
IN 01 ;GET CHAR
000B 77
MOV M,A ;SAVE IN MEMORY
000C
23 INX HL ;ADVANCE
MEMORY
000D C30300 JMP $0003 ;LOOP BACK
FOR NEXT CHAR
After you toggle it in, you can reset and run, then have
your PC send binary characters to be stored at address $0010 and up.
I was
using a small VB program I wrote that just opened a binary file and sent the
bytes. There's no error checking, but it worked well enough to get a basic
monitor into RAM. I also wrote up a decent monitor that includes
XModem. I'll send this as an attachment. You will need to assemble
it. You can delete the Floppy Disk section, since that will only work with
the Tarbell MDL 1011 controller (or any other WD 1771 based FDD
controller).
I am assuming in this code that your SSM IO-4 is strapped
for Altair Mode (this was how mine is/was strapped when I got the
IMSAI).
After the file transfer is complete, reset the computer, replace
the first byte (21) with C3 to cause a Jump to $0010, then flip the run
switch. If you want to try loading my Monitor program in, then add
something like:
.ORG 0010h
JMP MAINMENU
Also, check where "MAINPROGRAM" equates to, this has
to point to RAM space.
That is so strange that all those 8080A's aren't
working for all codes... I am thinking something is still wrong with your
CPU and/or FP boards.
Perhaps try slowing down your clock? You
might be able to just drop a different crystal into the 8224 circuit. It's
expecting a series cut crystal, my knowledge ends here, so I can't say if a
parallel cut crystal would work, my guess is there's no harm in trying.
Toss in a 32Khz crystal, that should make for a nice and slow system, then you
can definitely scope for bus noise, or
contention.
From: er...@osmancrew.com
To: n8vem...@googlegroups.com
Subject:
RE: [N8VEM-S100:1495] New/Old Project (Altair restoration)
Date: Sat, 9 Mar
2013 10:26:18 -0800
If that
yellow jack on the new TVs will work, then I should be fine, as we have a small
one that isn't being used, except occasionally in the guest
room.
I'd be
interested in your 16 byte bootstrap, if you're willing to share. My old
bootstrap was considerably longer and I'll need to do something along those
lines until I get some kind of ROM board going. Eventually, I'd like to
get to the point where it us using a virtual floppy or hard drive on
flash.
I took a
couple hours out last night to test four old 8080 chips I had lying
around. The one I've been using is a recent purchase from Jameco, an
actual Intel part, amazingly enough. Anyway, they all "kind of"
work. In other words, they will properly execute some instructions and not
others. I found this surprising. I would have thought they would
either not work at all, or work 100%.
Eric,
I totally understand
time restrictions on these projects. I thought it would take me 4 months
to get my IMSAI running, but between family, work and other projects it took a
solid 13 months and there's still more I'd like to do. It's like every new
idea spawns two more. Even interest in this hobby waxes and
wanes.
I'm aware that new TV's no longer have the analog tuner but most
if not all of the new TV's I've seen still have a Yellow RCA jack for plain NTSC
video input. But, you probably don't want to use your main TV, instead,
try to sit your wife down in front of it with a chick flick while you tinker
with the Altair. For this purpose, it's not a bad idea to find an older
TV, something more retro to match the Altair. Or you can also find
security monitors, they all take standard video in. Check your local
craigslist listing, I'm sure you'll find many bargains. I also see many
old TV's for $10 or less at garage sales.
PS. I also have a SSM IO-4
card. Getting your system to boot up will require a monitor in ROM, or
some kind of floppy disk system. The ROM card is cheaper, Rich Cini uses a
similar approach, if you search the forum or his site you can find more info on
the RAM/ROM card he's using. It's a very cool board, because it lets you
pop out the 2K RAM chip and replace it with a 2K ROM chip for that part of the
memory map.
Before I got my system to boot, I would toggle in a 16 byte
boot strap to load programs from the PC. It's fun to do the first dozen
times, then it gets old and you start to wonder how much wear and tear you want
to put on your switches.
Regards,
Josh
From: er...@osmancrew.com
To: n8vem...@googlegroups.com
Subject:
RE: [N8VEM-S100:1491] New/Old Project (Altair restoration)
Date: Wed, 6 Mar
2013 21:17:22 -0800
Your
suggestion to clean the edge connectors and slots is a good one and I will be
doing that soon. I'm going to have to reduce the time I spend on this
project for a while so I can get my taxes done and do some other things to keep
the wife happy. But I still plan to try to put 3 or 4 hours a week into
it.
Here's a
question: The Processor Technology VDM-1 puts out composite video.
My old TV with composite video input is long gone. What do people
recommend for converting composite video into something a modern monitor can
use?
That SBC
you're putting together looks pretty ambitious. It will be interesting to
see the circuit diagrams when you get done. Maybe I'll build a
copy one of these days. But first, of course, I need to finish
getting all my current hardware working, which will be quite a project in
itself:
o
Another Altair CPU card
o Two
Processor Tech 4K SRAM cards
o A
processor Technology VDM-1
o A
Thinkertoys 32K SRAM card
o A
Solid State Music IO-4 card
Then
there's the matter of setting up some way of booting something useful, even just
a monitor, with a minimum of switch flipping. I'd forgotten how tedious
and error prone that is.
Hey
Eric,
You made a good point about testing the RAM for hours. I only
ran my tests for a few loops, not more than 30 minutes, but I should be testing
it like you are doing for a solid 24+ hours.
I find the edge card
connectors need a good scrubbing, and you gotta get into the S-100 edge card
sockets too. I wrote about this recently, if it was to you, then forgive
me for repeating. To get into the sockets, cut one of those white rubber
erasers into 1/16" thick slices and press it in and out of the socket, be sure
to brush, vacuum and blow the sockets clean afterward.
This is great that
you've got a good point to start from. It can be very frustrating when
everything that can go wrong has gone wrong.
I had a weird (conditional)
problem on my I/O card, but lost my patience and replaced 6 possible
chips. I fixed the problem but didn't learn anything in the
process.
I just recently powered up a home brew 8080 card for another
IMSAI I'm working on. The cpu didn't work right away, there were
issues. FIrst it was the ready line that wasn't Active due to an I/O
interface latch, next I found that I didn't wire the HOLD and INT lines, so they
did go Active! Then another chip didn't have VCC connected, got that working but
the CPU control (Examine/Deposit) didn't work (added some more logic to disable
the RAM while operating the CPU). Lots of little problems, but I can't
tear myself away from working on it, too damn addictive! Look for another
post to Andrew for more details on this card if you want to see
pictures.
Cheers,
Josh
From: er...@osmancrew.com
To: n8vem...@googlegroups.com
Subject:
RE: [N8VEM-S100:1488] New/Old Project (Altair restoration)
Date: Tue, 5 Mar
2013 21:05:42 -0800
Well
that 32K RAM card didn't work out as well as I hoped. It failed a
memory test sporadically so I decided to concentrate for now on my good,
old 1K RAM card from MITS. After tracking down several problems with the
support logic, I just went ahead and replaced it all. Then I wound up
replacing one of the RAM chips. When running diagnostics it would stop
with a dropped bit after anywhere from 2 to 6 hours and this would occur on any
of the RAM chips, including the one I replaced. Always bit zero. I
was running this diagnostic on the 1K card with the 32K card still in the
system. I decided to remove the 32K RAM card and move the 1K card right
next to the CPU. It has now run over 26 hours with no dropped bits,
although it has stopped twice when the memory protect turned on by
itself.
So I'm
thinking I have a noisy bus and will need to do something about that before I
can make more progress toward a reliable system. I have a terminated bus
on the way, but it will be a few days. Then I'll have to use a proto card
to hook the front panel into the bus. All 70 wires, approximately.
Yuk.
I hear
what you're saying about the older memory cards being unreliable. I hope
I'm able to get mine working because I'd like to keep the system as close to
"original" as possible. Of course swapping out the bus isn't exactly
original, but that old Altair bus really sucks. Alternatively, I could try
adding a terminator card to the end of the Altair bus.
Once I
have a reliable system, even with just 1K of RAM, I'll have a known good base
from which to start trying to fix the other cards.
Thanks
for all your help.
Hi Eric,
Excellent work!
Yes, you are right about the RESET line needing
to be low, sorry that was my mistake. I thought it was a "NOT" RESET line,
that's why I put an asterix after the name RESET*. FYI, In the old S-100
bus descriptions, an asterix indicates a "NOT" logic pulse, eg Pin 77 is pWR*
for "NOT" Write.
My IMSAI also has a noisy o1 and o2, see picture
attached.
Perhaps you can improve your wave forms by adding some decoupling
capacitors near the clock?
You might have dirty edge card
connections. Get a nice white polymer eraser and give the pcboard fingers
a good scrubbing. I even slice the eraser into pcboard thickness and press
in to the connectors. Just be sure to fish or blow out all the
rub-off.
On the IMSAI, I tried several memory boards, they all were
flakey. I had to build a new RAM card with modern chips. Later RAM
tests confirmed my suspicions on those old memory boards.
But, overall it
sounds like you are well on your way to fix everything. Looking
Good!
Regards,
Josh
From: er...@osmancrew.com
To: n8vem...@googlegroups.com
Subject:
RE: [N8VEM-S100:1476] New/Old Project (Altair restoration)
Date: Wed, 27 Feb
2013 19:51:09 -0800
I went
through all the checks you suggested and everything looked good. The only
exception is that I found reset on pin 12 to be low instead of high. This
is what I would expect based on my reading. Was that a typo, or am I
missing something?
Some of
the waveforms were a bit ratty, but OK, I guess. I don't want to clutter
everyone's inboxes with a bunch of pictures, so I'm only attaching one. It
is of the two clock phases on pins 15 and 22 of the CPU chip. This was a
real eye opener to me a relative neophyte. Not the pretty square waves
they show in the book, that's for sure.
After
replacing the one 8T97 and getting much better voltages on the bus associated
with those lines I went ahead and replaced all of them all and viola, I have a
CPU board that seems to work! The front panel functions seem to work as
well.
I
plugged in a recently acquired 32K static RAM board and everything seemed to
work except that I could deposit to memory using the front panel, but the CPU
did not seem to be able to write to memory. However, it started
working when I plugged the memory card into a different slot.
Spooky. I haven't yet put it back in the original slot to see what happens
but this seems like a problem I'd better get to the bottom
of.
I also
have another CPU card and a few RAM cards to get working.
Thanks
again for all your help.
Hi
Eric,
That does sound like good news. Those 8T97's on the 2nd CPU
board might be the issue there.
Sockets on all the chips shouldn't make a
big difference, just as long as they are decent sockets.
The only very
sensitive chip that you might not want to socket is the Crystal Oscillator chip,
7404.
How's your soldering? did you give a good visual for solder
shorts? I like to hold the board up with a bright light behind so the
board glows, you can see solder shorts and/or micro shorts.
That's
wonderful that you have a 2nd board. Now you can compare signal
pulses between them. Go pin by pin on the CPU board, make your notes or
take pictures.
Yes, it does eat lots of time. I have the same
frustration with time. Every project turns into hours, but I love doing it
so those hours pass by so fast! But rest assured, you will find the
problem(s) and fix if you keep studying the schematic, datasheets, etc The
victory in the end is worth it!
:)
Cheers,
Josh
From: er...@osmancrew.com
To: n8vem...@googlegroups.com
Subject:
RE: [N8VEM-S100:1471] New/Old Project (Altair restoration)
Date: Mon, 25 Feb
2013 11:59:49 -0800
Thanks
for all the pointers and ideas.
Voltage
levels to CPU chip OK.
I wired
up a proto board to pull the DI lines low for the NOP test as you
suggested. Going through a 100 ohm resistor didn't seem to successfully
pull the lines low, so I tied directly to ground.
I still
observe very flaky behavior with that CPU board that I can't begin to
characterize. You've got me wondering if those sockets I put on that board
were a good idea.
I have
another used Altair CPU board I bought a few years ago in anticipation of this
project. When I tried it the address bus does "count" as you suggest, but
that board has its own problems. I can stop the processor and reset.
Examine next seems to work, if I look real close at the lights. This got
me to checking the voltage levels on the address bus (with the processor
stopped). "High" is in the range of 1V. "Low" is in the range of
0.1V. This varies a bit from one address line to the next. For some
lines "high" is in the range of 1.5V which is enough to actually light the LED
on the front panel. Recall that with the first CPU card (the one I
rebuilt) I was seeing more like 3.4V. I verified that the addresses output
to the 8T97 from the CPU chip are in the +5V range. I notice the 8T97
seems to be getting fairly warm so it must be dissipating all that voltage
internally for some reason.
My
current plan is to pull one of the 8T97s from this CPU and put a socket in there
to see if a new 8T97 works better. If I can get a known working CPU I feel
like I can begin to debug any problems I may have on the front
panel.
Fun
stuff. Eating lots of time.
Thanks
again. I really appreciate your help.
Hi
Eric,
Yes, you must have the front panel in place. It is required
to put the CPU in a "RUN" mode. The front panel controls or generates the
CPU mode (RUN, WAIT or RESET). The 2 lines of interest are the pRESET (pin
75 on the S-100) and XRDY (pin 3).
Other S-100 lines of interest are pRDY
(pin 72), and pHOLD (pin 74).
When running the NOP test, you want to
scope every pin on the CPU to understand what it's doing.
Look at the timing
diagrams of the 8080A data sheet.
1st check the voltage pins (good idea to
check ground pin 2 with ohm meter prior to powering system).
2nd check the
CPU clocks, Pin 22 & 15 should have non-overlapping positive pulses to
12V. These are not TTL inputs.
3rd check the CPU mode, Reset* pin 12
must be high, Ready pin 23 must be high, Hold pin 13 must be low, INT pin 14
should be low.
The mode inputs should be steady, no pulses.
4th check the
CPU timing output pulses. WR* pin 18 should be high (we're executing
NOP's, there should be no memory writes), DBIN should be pulsing high to
fetch/read the NOP instructions, Sync pin 19 should be pulsing high during M1 of
every cycle as per the data sheet.
5th Scope your data lines, these should be
LOW (as tied low for the NOP) during the DBIN pulses, some pins should pulse
high during the PSYNC to indicate M1 and sMEMR cycles (read the data
sheet).
6th Scope your address lines, these should be counting up, you should
see them all toggling high/low. Follow this signal onto the S-100
bus.
The advantage of running NOP's, is that the CPU wave forms are
repetitive and easy to follow on the scope.
Also, it eliminates all other
memory and I/O boards, breaks your system down to the basics.
See CPU
run.
Run CPU run.
Once you can get this far, it's likely that your
system will operate if the other boards are good.
But getting here isn't
always so easy.
I did a similar test to fix my OHIO Superboard. It
was working intermittently with the NOP test. The problem was bad sockets,
to make things a challenge, when I would scope a pin, the pressure put on that
pin would make it temporarily connect. I think the Altair used good
quality sockets, but best to keep your wits about you!
Please keep in
mind that I'm running an IMSAI 8080, but I think it's almost an identical copy
of the Altair.
Cheers,
Josh
From: er...@osmancrew.com
To: n8vem...@googlegroups.com
Subject:
RE: [N8VEM-S100:1452] New/Old Project (Altair restoration)
Date: Sat, 23 Feb
2013 21:54:57 -0800
I assume
I can leave the front panel hooked up for the NOP test? I dread the
thought of removing and replacing all those wires again.
I
actually have three different 8080 chips and the computer doesn't work with any
of them, although the symptoms change slightly. In any case I have a new
one on order "just in case". It is true that none of the three are
"known good", so I like the idea of this test, I just hope I can do it with the
front panel in place.
Hi
Eric,
Very cool!
I have an IMSAI 8080. I checked the address
lines and I also get 3.43V. Using 8T97 chips.
You are right about
the LS chips not being an exact replacement for the standard chips.
They will
work well enough as drop in replacements for digital circuits, but a crystal
oscillator is an analog circuit.
I have seen such oscillators fail with same
part numbers by different manufacturers.
That same oscillator circuit even
failed by simply installing a socket. Trust me, I didn't believe it at
first but after installing and removing it a few times, I recognize that crystal
oscillators using TTL are very sensitive.
Lee Hart has taught me that CMOS
chips make much better choices for crystal oscillators.
Back to your
Altair. The 3.4V should work fine, it does on my system.
The ring looks
big, but I don't believe it's beyond a reasonable amount for a functioning
system.
You can probably reduce the ring by terminating that line, but it's
quite likely you don't need to.
May I recommend a "NOP" test?
Remove all boards except the CPU. Pull the DI0-7 lines low. Ground
them or use 100 ohm. There shouldn't be anything driving those DI lines,
so be suspicious if you read voltage on those lines.
This is the NOP command,
let the CPU run, now scope all the lines. Look for pSync, o1, o2, clock,
MEMR, DBIN. The address lines should be counting. Check your CPU for
correct voltage, check the WAIT, HOLD and RESET signals. Your CPU must be
running, if not, then you have a bad CPU chip. If anything isn't right,
trace the signals back to the front panel switches. Check that DI0-7 is
reaching the CPU through the buffer chip.
I hope that idea helps. good
luck.
Josh
>
From: er...@osmancrew.com
> To: n8vem...@googlegroups.com
>
Subject: RE: [N8VEM-S100:1447] New/Old Project (Altair restoration)
>
Date: Sat, 23 Feb 2013 20:07:43 -0800
>
>
> With advice from
Tom Lafleur and others I've been making some progress on my
> Altair
restoration. This machine was killed by a lightning induced power
> surge
many years ago. I've installed new, modern power supplies, and I've
>
removed all the chips from the front panel and the CPU. These were
replaced
> with sockets. I learned that apparently, you can't always
replace 74xx with
> 74LSxx. I learned this when the system clock would not
run when I tried two
> different 74LS04 chips in the clock circuit but
works fine with a 7404.
>
> Anyway, after repopulating the chip
sockets with mostly LS parts, the Altair
> exhibits very strange and
unstable behavior. I almost don't know where to
> begin to describe it.
Let's just say that the results of a reset are fairly
> random.
>
> I thought I'd ask a few specific questions:
> If I "stop" the
Altair and check the voltage of an address line on the bus
> that is high,
I get about 3.4 volts. The only boards in the system are the
> front panel
and the CPU. In this configuration, all that's going on is the
> 8080
address lines are buffered through 74LS367?s onto the bus. The front
>
panel is involved only insofar as the address lines each go through an
LED
> and a 220 ohm resistor to ground to display the address line's
state. Hard
> to imagine a simpler situation. The output from the 8080 is
a healthy 4.9V
> where it goes into the 74LS367, but on the output side it
is only 3.4V.
> This low voltage value for a high logic state seems like a
potential problem
> to me. Am I right?
>
> Lest you think it
might be a bad 74LS367, be aware that I previously had the
> functionally
equivalent 8T97 chips in there and had essentially the same
>
result.
>
> Also, the CPU and front panel regulators were replaced
and I get a healthy
> 4.96V on the +5 side of the regulators.
>
> So the immediate questions are:
> 1. Am I right in saying that
the 3.4V level is an issue?
> 2. If so, any ideas what could be causing
this?
> 3. I'm attaching the oscilloscope trace of the system clock as
seen on bus
> line 49. Does that look OK, or is there too much
ringing?
>
> CPU Schematic here:
> http://www.s100computers.com/Hardware%20Manuals/MITS/8080%20CPU%20Board%20Sc
>
hematic.pdf
>
> Thanks for your ideas.
>
> - Eric
Osman
>
> -----Original Message-----
> From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com]On
>
Behalf Of Eric Osman
> Sent: Saturday, February 02, 2013 12:48 PM
>
To: n8vem...@googlegroups.com
>
Subject: RE: [N8VEM-S100:1357] New/Old Project
>
>
> Douglas
-
>
> Thanks for the introduction and summary. I'm on Andrew's list
for an
> extender, and I'll probably be looking to obtain a prototyping
card as well.
> These are driven by my initial goal, which is just to get
my Altair working
> again. Longer term I'll be looking to enhance it a
bit.
>
> I was intrigued enough by the Raspberry Pi to get one, but
of course, that
> is not the focus of this board.
>
> I'll be
looking over the Wiki's and mail group archives that you mentioned.
>
> Thanks again.
>
> - Eric
>
> -----Original
Message-----
> From: n8vem...@googlegroups.com [mailto:n8vem...@googlegroups.com]On
>
Behalf Of Douglas Goodall
> Sent: Saturday, February 02, 2013 10:52
AM
> To: n8vem...@googlegroups.com
>
Subject: Re: [N8VEM-S100:1355] New/Old Project
>
>
>
Eric,
>
> Our group consists of lots of old-timers and youth as
well.
>
> Apparently all of us like to fiddle with hardware, and
there is quite a lot
> of fun going on.
>
> The major
interests within the group are focused on a range of hardware, as
> simple
as a single
> board computer (See the Zeta), and more sophisticated buss
oriented systems,
> both S-100 and ECB.
>
> Andrew supplies
bare circuit boards for us, mini boards, SBC's, and a highly
> integrated
machine we
> started calling the N8 (originally named "Home
Computer").
>
> John sells S-100 bare boards, CPU cards, memory
boards, ...
>
> There are two main Google mail groups, one for
Andrew's focus
> (n8...@googlegroups.com) and one
>
for John's (n8vem...@googlegroups.com).
There is another one recently
> formed for the scsi to ide
>
project, aka S2I.
>
> Information about the boards, schematics,
board layouts, etc are found on
> the wiki
(n8vem-sbc.pbworks.com).
>
> Building these boards is a learning
experience, and we gain knowledge about
> sourcing parts, building
up
> boards and then debug them. The community members are very happy to
help
> each other get things working
> the google groups are a
constant stream of questions and answers about
> aspects of the hardware
and
> software.
>
> There are a number of different BIOSs
written by community members, some of
> which are more specific
and
> some of which are more productized and full featured. If you want to
find
> out more about the boards, look
> under board information on
the wiki. There is a software information section
> as well.
>
> Welcome to our community, and don't be shy to communicate with us via
the
> lists or privately.
>
> Regards,
>
>
Douglas Goodall
>
> On Feb 2, 2013, at 1:23 AM, Eric O <ewok...@gmail.com> wrote:
>
> > Andrew Lynch suggested I join this group and seek assistance with
my
> "project".
> >
> > Background:
> > Back in
1975 I was a 20 year-old electrical engineering college student
> and
electronics hobbyist and saw the famous Popular Electronics article on
>
the Altair 8800 computer. I ordered it, assembled it and it worked great
as
> soon as I powered it on for the first time. Over the next year or
three I
> enhanced it with some additional memory, a homebrew parallel and
serial
> interface and the Processor Technology video card. I wrote
hand-assembled
> machine code to "boot load" my own little monitor via a
modem to the
> mainframe computer on campus. This involved an automated
log-in to my
> account, starting the listing of a hex file and then
capturing and loading
> that hex file into the Altair RAM. Of course I had
to switch a couple
> hundred bytes of machine code into the Altair
whenever I needed to "reboot".
> I also wrote a terminal emulation program
so I could then use it as a
> terminal to that same mainframe. Great fun
and done on a shoe string
> because I was a very poor college
student.
> >
> > Disaster literally struck out of the sky one
day around 1979 when a very
> powerful thunderstorm hit and a lightning
bolt literally blew the top off
> the power pole that fed the off-campus
house I shared with three other
> students. I should have unplugged the
Altair when the thunderstorm arrived,
> but I didn't want to have to take
15 minutes to reboot it. Stupid! Anyway
> the power surge killed the
machine. It would still light up but it wouldn't
> do anything approaching
normal operation. I did replace a number of the
> chips in the weeks that
followed, but I couldn't afford to do a proper job
> of it.
>
>
> > Well, graduation came, then a job, then an IBM 5150, and then
other
> computers over the decades and now the Altair has been stored in a
box for
> almost 35 years. I always meant to fix it someday but never got
around to
> it. But now that I'm semi-retired from a career in computers
I'm finally
> getting around to it. So a couple months ago I finally got
it out of that
> box and started doing a bit of research and I'm so happy
to see all the love
> that people have for these old machines.
>
>
> > One of the first things I learned was not to trust the
original power
> supply. So I went out and got a couple switching power
supplies from
> MeanWell, mounted them up in the chassis, and leaving the
old supply
> physically in place, removed it electrically and replaced it
with the new
> supply.
> >
> > I popped out all the
boards, and turned it on. I'm getting all the proper
> voltages in all the
proper places, including regulated +5.13 on the display
> board. With the
CPU in I get the proper regulated voltages on the CPU card:
> (-5.25 on
Pin 11, +11.69 on pin 28, +5.00 out of the regulator).
> >
> >
I've started working on the front panel and I've already identified two
>
inverters with the same logic state on each side of the gate, on two
>
different chips. So I know I need to replace those.
> >
> >
Any and all suggestions welcome.
> >
> > (I've seen the very
good article at
> http://s100computers.com/My%20System%20Pages/Debugging/Debugging%20for%20beg
>
inners.htm)
> >
> > Eric O
> >
> >
--
> > You received this message because you are subscribed to the
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> >
>
>
>
> ---
> Douglas Goodall, http://goodall.com
>
> Note: I don't use
messenger, or skype, or facebook, chat programs in
> general. Having
always-on open communication links through massive public
> servers I
don't have control over seems like too much of an invitation to be
>
infected by a virus or bot. It is bad enough that my Mac wants to stay
in
> periodic contact with Apple's cloud. Skype was tempting before
Microsoft
> bought them. There have been too many examples of remote
session links being
> abused by vendor employees. Even "back to my mac"
makes me nervous. There
> was a recent episode where Apple cooperated with
a social engineer and
> compromised someone's entire electronic persona.
If you want to speak with
> me, calling me on the phone works well, and
you don't have to wonder if the
> electronic mail got through or not. When
I say "Hello, this is Doug", you
> know who you are talking to. Just in
case you were curious.
>
> --
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