5 Mar
1998
5 Mar
'98
4:10 p.m.
OK, I've kind of settled on an approact to restoring the DL8A. I figure I'm
completely unqualified to do any of this and so will rely upon advice and
help from those of you who are.
I think the first and most important step is to back-up the extant 1702 boot
program. I've been thinking about this one (re: bit rot); would it be
possible to get a disassembly of the code to see if it looks OK? It can't
be too big - only 4 eproms total. Does bit rot proceed on a bit-by-bit
basis, or are whole segments knocked out at a go (ie: bytes/multiples)? I
presume that it will be possible to restore the boot program if there is
some significant part of the eproms intact - opcodes anyway...
The disassembly should give some clues as to operation of the machine, too.
So, firstly I ask if anyone with a 1702 programmer who would be prepared to
handle copying these 4 eproms for me to wave their hands in the air. I'll
also need 4 of the 1702 eproms, so would appreciate anyone with those to
also wave their hands. And finally, I'm looking for a PC based 8080A
disassembler. My plan is to pull the chips and airmail them to a kind
volunteer. Actually - although I don't have a lot to spend - I will be most
happy to pay for the preservation (restoration?) of these data. I think its
important.
I do believe this machine is possibly unique; certainly rare - and worth
restoring properly. I would note that the cosmetics are near flawless;
this bodes well for the electronics inside, no?
Cheers
A
5 Mar
5 Mar
5:24 p.m.
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6 Mar
6 Mar
8:32 a.m.
At 11:24 PM 3/5/98 +0000, you wrote:
Trouble is, he's in Australia not in the US. The ROMs are going to have
to be shipped unless someone in Au has a 1702 reader.
So, firstly I ask if anyone with a 1702 programmer who would be prepared to
I'd rather not do this, not because I don't want to help you, but because
I'd be a little worried about sending 4 irreplaceable eraseable chips
through the post. I would hope somebody Stateside could help you. You probably don't need to make a copy _now_. Just
make sure the EPROM
images are backed up onto something permanent (paper tape ? :-)). Then
somebody can burn you a copy in the future if you need one.
He had ALSO better back it up to something newer than a paper tape, paper
tape readers are getting hard to find. In fact, since 1702s and
programmers for them are getting rare, I think someone should engineer a
1702 replacement out of modern ICs that can be programmed on a modern
equipement. Then match the storage media to that equipment. Given the
rapidly dropping cost of recordable CDs, I think it whould be worthwhile to
record the code on that. They should last nearly forever.
Joe
6:11 p.m.
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10:12 p.m.
At 12:11 AM 3/7/98 +0000, you wrote:
I thought most members of this list had a pair of optical paper tape readers
fixed in their faces :-)
Yes, but my optical readers never were that good to begin with and they
certainly haven't improved with age :-( And the memory that it's connected
to acts like a buffer, FIFO, if you know what I mean.
Trouble is,
he's in Australia not in the US. The ROMs are going to have
to be shipped unless someone in Au has a 1702 reader.
I supose the solution is for him to build a 1702 reader (which is a lot
simpler than the programmer!) and to read the EPROMs himself. The problem
is that the 1702 uses at least one strange voltage (a -9V supply, I
think), and if you make a mistake when building the reader you could ruin
the very chips that you're trying to save.
The ultimate solution would be for somebody to program a 'spare' 1702
with a known byte sequence, and use that to test the homebrew reader. A
lot of work, though.
I am still a bit worried about sending irreplaceable chips by mail. I've
had a number of old computer bits sent to me, and AFAIK there have been
no problems - in fact the Customs haven't even opened the packages. But
murphy's law states that the package that contains those EPROMs will be
the one that's suspected of being a bomb and blown up, or the one that's
X-rayed with a sufficient dose to damage the chips, or the one that's
lost, or whatever.
You probably don't need to make a copy _now_.
Just make sure the EPROM
images are backed up onto something permanent (paper tape ? :-)). Then
somebody can burn you a copy in the future if you need one.
He had ALSO better back it up to something newer than a paper tape, paper
tape readers are getting hard to find. In fact, since 1702s and
Seriously, good paper tape reading machines are going to last almost for
ever - there's not a lot to go wrong with them. And I'm quite sure
there'll be _somebody_ with one in the future.
Perhaps in a museum.
I didn't mean that paper tape should be the only backup - keep a copy on
disk, on CD, on DAT tape, on whatever. Hopefully it will remain useable.
Use it as an image to disassemble, and to make replacement EPROMs. But
having a copy on a known-almost-permantent storage medium can also be useful
Except that -9 V is still sitting there.
programmers for them are getting rare, I think
someone should engineer a
1702 replacement out of modern ICs that can be programmed on a modern
equipement. Then match the storage media to that equipment. Given the
It's called a larger EPROM with the higher address lines tied to ground :-)
2764's are so cheap now that it's worth using one as a 256 byte (or 1K,
or whatever) EPROM and wasting most of the chip.
That's what I mean, just a piggy back board to change the pin out of a
2764 (or something similar) to mathc the 1702 socket. 2764s are definitely
easier to find and cheaper than 1702s!
Making up an adapter board shouldn't be hard apart from the fact that the
1702 doesn't have a ground connection. The simplest way to deal with that
is to have a flying lead on the adapter board that you solder to a 0V pin
in the computer. Hardly original, but then nor is using the 2764 in the
first place.
I suppose you _could_ put a 9V1 zener diode in series with the -9V
supply to drop the 9V. I'd also connect a 1k resistor between the power
and ground pins at the EPROM if I did this, to ensure that there's enough
current flowing for the zener to work correctly. Maybe I'll try it sometime.
Good point but I can BUY a CD drive for less than it would cost me to
move my KSR-33! Actually if you're dealing with a 1702, it's small enough
that you can just write the code down! And paper is paper!
BTW went to a surplus auction at a nearby air force base yesterday. They
had some of the old familar yellow teletype paper for sale! (Hell no, I
didn't buy it! I would just as soon never see another teletype!)
Joe
rapidly dropping cost of recordable CDs, I think
it whould be worthwhile to
record the code on that. They should last nearly forever.
Hmm... I'd rather trust paper tape than a CD. And a paper tape reader is
going to be a lot easier to repair than a CDROM drive - getting spares
for those is, in general, non-trivial as I found out. And when was the
last time you saw a CD-ROM drive service manual? 
11:46 p.m.
Joe wrote:
Good point but I can BUY a CD drive for less than it
would cost me to
move my KSR-33! Actually if you're dealing with a 1702, it's small enough
that you can just write the code down! And paper is paper!
The monitor for my Lawrence Livermore MST-80b resides on a pair of
1702s. But I have the manual which contains a source listing ;) And
the system board has an empty 24 pin jumpered socket that can be mapped
to accomodate a larger, more modern EPROM *and* access the monitor from
there... I assume this is the sort of thing they had in mind when
providing that socket in that way. I don't wish to tinker too much with
this thing, so that is something I'll probably only ever do in a real
pinch.
--
mor(a)crl.com
http://www.crl.com/~mor/
7 Mar
7 Mar
11:58 a.m.
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5 Mar
5 Mar
5:45 p.m.
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6:50 p.m.
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9804
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9806
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8 comments
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participants (5)
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adavie＠mad.scientist.com -
ard＠p850ug1.demon.co.uk -
mor＠crl.com -
rigdonj＠intellistar.net -
shoppa＠alph02.triumf.ca