"New" PDP-8

From: Loboyko Steve <sloboyko_at_yahoo.com>
Date: Sat Mar 30 12:01:12 2002

Well, other than a few extremely minor hardware
changes, I did -absolutely- no design work on this, Mr
Armstrong did over the course of many years!

How it worked was this:

1. He has a PDP8 emulator for Windows, which does
emulate an RK05, and also the RAM chips in the "real"

2. He wrote device drivers for the RAM and the IDE
drive in assembler, which you assemble with PAL8 and
put on an emulated RX01 so that the RAM disk can be

3. Then, you SYS one of the RAM disks with the RAM
disk bootable.

4. Then, you download that RAM image to the BTS6120
(single board PD8) and boot from that.

4. Then, you sys the IDE drive in the physical BTS6120
design so that it is bootable.

5. Then, you copy stuff from the RAM disk in the
emulator to the RAM disk in the BTS6120, and repeat.

So, the RAM and IDE drives are "legitimate" OS8
devices. The IDE is broken up into 8 partitions of
about 2 MW each (so even the oldest IDE drive that
supports LBA, which any drive over 600 meg probably
does) will work. I used the 2.5" drive only for space
and power reasons.

An additional complication was that the 512Kx8 ram
chips in the original design (static, low power) were
quite expensive for four of them so I used 128K ram
chips that I got on a good deal instead. So I had to
cut 3/4 of the disk image off(after "squishing" -
packing the disk of course) before downloading. So I
had to repeat (5) above several times.

It took me almost as long to figure out how to do this
as it did to build it. Mr. Armstrong was as helpful as
he could be but there was no substitute for "pounding
it into submission".

On the 6120 chips (I don't think you could use 6100
chips in this) - I got mine socketed in a DECmate CPU
board for $25.00. I'm getting a few as a spare. A drag
about the DECmate board was that its a multilayer
board, and in spite of my best desoldering efforts,
the chips are trimmed short and you can't really use
many parts from it other than the socketed BTS6120 and
a few EPROMS. Bob Armstrong has PCB's available but
they are pretty expensive because they are multilayer
and lets face it, he can't have hundreds made at a
time. On the other hand, I paid myself about $5.00 an
hour wire wrapping instead!

--- Heinz Wolter <h.wolter_at_sympatico.ca> wrote:
> Being a hardware guy - I want to know - did you (or
> Mr. A)
> fully emulate a DEC drive (RK05??) or other drive
> with a microcontroller ? or did you write a device
> driver to support the IDE drive under OS8? Either
> trick would
> be very slick indeed ;)
> Regards and congratulations on getting your baby
> running.
> Once and a while you see these Intersil 61xx chips
> appear
> on ebay.. maybe others could duplicate your
> efforts..
> Cheers, Heinz
> Re:
> From: "Loboyko Steve" <sloboyko_at_yahoo.com>
> Subject: "New" PDP-8
> > I just completed the very nasty job of downloading
> the
> > operating system and a few BASIC programs to my
> "new"
> > PDP8, which is built from Robert Armstrong's
> design.
> > It only draws about 5 watts, so it isn't a problem
> to
> > keep on all the time, unlike others that people on
> > this list might own!
> >
> > I made a comment to Mr.Armstrong that I removed
> the
> > IBM logo from the drive because I didn't think it
> > would work correctly with a DEC design. Strangely,
> > this actually came true to a degree; I had a slow
> > chip that didn't get data from the drive quickly
> > enough. I tried to save a dollar buying an 82C55
> > instead of an 82C55-5.

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Received on Sat Mar 30 2002 - 12:01:12 GMT

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