Digital archaeology of the microcomputer, 1974-1994
By Steven Goodwin <http://www.freesoftwaremagazine.com/user/39>
/Online on: 2007-01-05/
/(Or, how to prevent the Dark Ages of computing through free software)/
In a few years time, it will be impossible to study the history of home
computers since everything at the time was proprietary; both in terms of
the physical hardware, and all the software that ran upon it since most
of it is encumbered by software ?protection? to prevent copying.
To compound the problem, the hardware is dying (literally) and (being
proprietary) can?t be rebuilt in any equivalent manner. In some cases
the software is physically disintegrating too since, in the case of many
8-bit micros from the 1980?s, the storage medium was cassette tape; a
temperamental mechanism at the time, let alone now. It?s not that no
computer innovation took place in the 1980?s, just that none of it will
be recorded.
<snip>
http://www.freesoftwaremagazine.com/blogs/digital_archaeology_of_the_microc…
ah, charcoal gray, CX5. Models with or without the
synthesizer. What about in Canada?
--- cctalk-bounces at classiccmp.org <cisin at xenosoft.com>
wrote:
> It was a Yamaha, but I don't remember what model.
>
> On Sat, 20 Jan 2007, Chris M wrote:
>
> > which one?
> > --- cctalk-bounces at classiccmp.org
<cisin at xenosoft.com>
> > wrote:
> > > We bought an MSX machine from Mitchell Waite.
> > > They were trying to decide whether it would be
worth
> > it to publish an MSX
> > > book.
> > >
> > >
> > > --
> > > Grumpy Ol' Fred cisin at xenosoft.com
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ah, charcoal gray, CX5. Models with or without the
synthesizer. What about in Canada?
____________________________________________________________________________________
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which one?
--- cctalk-bounces at classiccmp.org <cisin at xenosoft.com>
wrote:
> We bought an MSX machine from Mitchell Waite.
> They were trying to decide whether it would be worth
it to publish an MSX
> book.
>
>
> --
> Grumpy Ol' Fred cisin at xenosoft.com
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Please forgive me for the marginal off-topic nature of this post. The
machine in qurstion is an HP9820, which is, I think, a programmable
calculator (the distinction being that it has a key-per-function type of
keyboard, not a full alphanumeric one where you type out the keywords).
But anyway...
I'm working on an HP9220,. For those who know nothing about this series
of machines, its one of the few common-ish bit-serial procesors (and is
intereting for that reason alone). The processor has 2 accumulators (A
and B), program counter (P), current instruction (Q -- stands for
'qualifier,' I am told), extension (E -- only 4 bits wide), I/O, memory
address (M) and memory data (T) registers. It's microcoded (256 28 bit
words). Binary operations are done bit-serially, BCD operations (which
have to be between the A and T registers, with the result going into A)
are done 1 nybble at a time. The ALU is actually a pair of programmed
PROMs, not 'normal' logic. Oh, nnd to add to the fun, the memory system
uses some odd voltages. The ROMs are HP custom chips with chip select
lines that have to be driven to +12V (all other I/O line are TTL
compatible). THhe RAMs are Intel 1103 DRAMs, they're PMOS and use 16V
logic levels with a further 3V bius supply on top of that (so there are
+16V and +19V lines to the RAM boards).
Anyway, the fault was 'no display'. That is not a suprise. Since the
display is software-scanned, almost all the machine has to be working to
get a display.
Well, I started off checking the PSU lines (actually with all the logic
boards removed), they were all fine. Then it's worth knowing that the
clock board will run on its own. If you power up just the clock board,
you get a muclock pulse (microcode clock) for every 16 bitclock pulses
(shift register clocks). That was fine too.
Now there are 2 ways to procesed. The hard and sure way -- look at
various signals, work out what the machine is doing, compare to what it
should be doing, and figure out what must be causing the problem. And the
easy and uncertain way -- it's a bit-serial machine so just about
everything should be changing. If something is stuck, that's a likely
place to start looking.
The M and T register bits are brought out on a test connector on the
memory box. So I looked there. It turend out that M(15) down to M(12)
were all toggling, the remaining 12 M lines were all stuck low. Rememebr
the M register is a 16 bit shift register, loaded from the MSB end. And
it's built from 4 7495 chips. So it seemed 'obvious' that the chip that
handles bits 11..8 had failed. It wasn't accepting data, it was providing
0's to the next lower chip.
Getting a replacement was not easy, but I mamanged it. Soldering it in
was trivial (pin-through-hole on a very well-made PCB). But would you
believe the fault was the same. Of course I'd checked the clocks and mode
control line were getting to all the chips in the M register.
Puzzeled, I looked again and M(12). It was toggling alright, but when I
sampled it with a logic analyser, I found high time of the pulses was
only the bitclock pulse high-time width. Which clearly can't be right for
a shift register made up of D-types clcokced form bitclock. Moreover
M(12) as always low just before the active edge of bitclock. so the next
shift register in the chain would always clock in 0's.
Out came the most significant nybble of the M register, and it was
replaced with the ship I'd removed ffrom M(11)..M(8). And the machine
then sprang to life.
So be careful. A signal can appear to be doing the right thing but can
have nasty timing problems...
-tony
> I can put these on floppies or if you know of a known good RX01/RX02
> image for a DECmate I can use it.
We have orig distribs for OS78 V4 and some DEC apps at CHM. I'll see about
reading them.
TMK the only *commonly* found MSX unit here in the US
was the Yamaha CX5, and I have that but never used it.
An interesting topic thats mostly foreign here.
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From: "Teo Zenios" <teoz at neo.rr.com>
> I was wondering what you people think about machines that have been
> used as a latrine by animals, do you clean them up or toss them?
Urine is very acidic (with acidity varying by type of animal), but by and
large it's just like any other acidic corrosive (smell notwithstanding). If
the damage isn't that bad, search the list archives for remediation. If
it's corroded the traces of the PCB, well, in theory you can patch it...you
make the call.
Almost any board that my cats manage to whiz on are usually totaled
> I hear rat excrement can carry some nasty deadly diseases.
Possibly, but you're probably thinking of mouse urine, which for certain
specific types of mice can carry hantavirus, at least in the Southwestern
US. Not good.
> OK, on closer look it appears as though these Eve drives might be
> ESDI/ST-506 and not SCSI. If they are ESDI, how could I archive them?
1) what were the drives connected to? If it is a custom controller you
either have to have enough knowledge about the machine to write a block
level dump program, or build something that can extract and then interpret
the data stream off of the disc. BTW, ST-506 is no easier than ESDI if you
are down at the bit level (other than the ESDI data separator was on the drive)
2) if it was a standard thing like a scsi to st506 or ESDI bridge board, things
are much easier. ESDI was new enough that bridge boards like the Emulex MD21
had inquiry commands so you can get the drive geometry. older boards require
the system to configure the board with that information, so you had to know
in advance what kind of drive is out there.
On Fri, 19 Jan 2007 19:18:17 -0500, Brad Parker <brad at heeltoe.com>
wrote:
> Someone approached me about some "prior art" and I am now looking at
> some 1/4" carts marked "quadra 950 retrospect 2.0 mac os" I made in
> the
> early 1990's.
>
> If somehow I could find a working 1/4" drive (scsi) and got it
> connected
> to a macintosh,
>
> Is there any hope I could find a copy of retrospect 2.0?
I have a couple of early copies of Retrospect - they are from 95 and
97, but don't label their version. I also have 4 and 5 available.
>
> anyone else ever try this?
You might want to find a SCSI tape deck that is currently supported
and then try a recent version (4 or 5) to attempt to read the tapes.
Dantz did a fairly good job of being able to read old backups with
current versions and I've pulled off some really old stuff when I was
using 4.
>
> it's probably hopeless, but it might be a fun ride. hard to say.
>
> good thing I saved that powerbook 145b :-)
Probably too early to do any good...
CRC
