Very cool. What did you use for memory?

73,

Dave, AA6YQ

"R J Carpenter" wrote in message
...

"Dave, AA6YQ" wrote in message
news:lARab.522300$YN5.348403@sccrnsc01...
No cheating! If you're going to homebrew a PDP-8, you have to build it
out
of discrete TTL.

I had my PDP-8S work-alike operational about 30 years ago. I built it
from
TTL.

"Dave, AA6YQ" wrote in message
news:7_vbb.546518$uu5.90927@sccrnsc04...
Very cool. What did you use for memory?

73,

Dave, AA6YQ

"R J Carpenter" wrote in message
...

"Dave, AA6YQ" wrote in message
news:lARab.522300$YN5.348403@sccrnsc01...
No cheating! If you're going to homebrew a PDP-8, you have to build it
out
of discrete TTL.

I had my PDP-8S work-alike operational about 30 years ago. I built it
from
TTL.

I bought a surplus IBM 1620 core memory stack from Burstein-Applebee. I
found a couple of the connecting wires were never properly soldered - which
must have been the reason for junking it. The 1620 had 10,000 12-bit words
of core. Actually every location had two 6-bit memory words. The 1620 was a
variable word length machine, with one bit of each 6-bit memory word being
the "word mark". I only used 4096 12-bit words of the memory, the normal
PDP-8 memory size. DEC's interactive FOCAL language allow easy programming
of simple problems. I also had their assembler.

The thing is buried in my garage, minus some big electrolytics.

73 de Bob w3otc

"Dave, AA6YQ" wrote in message
news:7_vbb.546518$uu5.90927@sccrnsc04...
Very cool. What did you use for memory?

73,

Dave, AA6YQ

"R J Carpenter" wrote in message
...

"Dave, AA6YQ" wrote in message
news:lARab.522300$YN5.348403@sccrnsc01...
No cheating! If you're going to homebrew a PDP-8, you have to build it
out
of discrete TTL.

I had my PDP-8S work-alike operational about 30 years ago. I built it
from
TTL.

I bought a surplus IBM 1620 core memory stack from Burstein-Applebee. I
found a couple of the connecting wires were never properly soldered - which
must have been the reason for junking it. The 1620 had 10,000 12-bit words
of core. Actually every location had two 6-bit memory words. The 1620 was a
variable word length machine, with one bit of each 6-bit memory word being
the "word mark". I only used 4096 12-bit words of the memory, the normal
PDP-8 memory size. DEC's interactive FOCAL language allow easy programming
of simple problems. I also had their assembler.

The thing is buried in my garage, minus some big electrolytics.

73 de Bob w3otc

Getting core memories to work was black magic with the original designers at
your side; that's something that you got a 1620 stack working on your own.
For the price of a few electrolytics -- or a new switching PS -- and a few
more hours, it definitely sounds worth resuscitating.

73,

Dave, AA6YQ

"R J Carpenter" wrote in message
...

"Dave, AA6YQ" wrote in message
news:7_vbb.546518$uu5.90927@sccrnsc04...
Very cool. What did you use for memory?

73,

Dave, AA6YQ

"R J Carpenter" wrote in message
...

"Dave, AA6YQ" wrote in message
news:lARab.522300$YN5.348403@sccrnsc01...
No cheating! If you're going to homebrew a PDP-8, you have to build
it
out
of discrete TTL.

I had my PDP-8S work-alike operational about 30 years ago. I built it
from
TTL.

I bought a surplus IBM 1620 core memory stack from Burstein-Applebee. I
found a couple of the connecting wires were never properly soldered -
which
must have been the reason for junking it. The 1620 had 10,000 12-bit words
of core. Actually every location had two 6-bit memory words. The 1620 was
a
variable word length machine, with one bit of each 6-bit memory word being
the "word mark". I only used 4096 12-bit words of the memory, the normal
PDP-8 memory size. DEC's interactive FOCAL language allow easy
programming
of simple problems. I also had their assembler.

The thing is buried in my garage, minus some big electrolytics.

73 de Bob w3otc

Getting core memories to work was black magic with the original designers at
your side; that's something that you got a 1620 stack working on your own.
For the price of a few electrolytics -- or a new switching PS -- and a few
more hours, it definitely sounds worth resuscitating.

73,

Dave, AA6YQ

"R J Carpenter" wrote in message
...

"Dave, AA6YQ" wrote in message
news:7_vbb.546518$uu5.90927@sccrnsc04...
Very cool. What did you use for memory?

73,

Dave, AA6YQ

"R J Carpenter" wrote in message
...

"Dave, AA6YQ" wrote in message
news:lARab.522300$YN5.348403@sccrnsc01...
No cheating! If you're going to homebrew a PDP-8, you have to build
it
out
of discrete TTL.

I had my PDP-8S work-alike operational about 30 years ago. I built it
from
TTL.

I bought a surplus IBM 1620 core memory stack from Burstein-Applebee. I
found a couple of the connecting wires were never properly soldered -
which
must have been the reason for junking it. The 1620 had 10,000 12-bit words
of core. Actually every location had two 6-bit memory words. The 1620 was
a
variable word length machine, with one bit of each 6-bit memory word being
the "word mark". I only used 4096 12-bit words of the memory, the normal
PDP-8 memory size. DEC's interactive FOCAL language allow easy
programming
of simple problems. I also had their assembler.

The thing is buried in my garage, minus some big electrolytics.

73 de Bob w3otc

"Dave, AA6YQ" wrote in message
et...
Getting core memories to work was black magic with the original designers
at
your side; that's something that you got a 1620 stack working on your own.
For the price of a few electrolytics -- or a new switching PS -- and a few
more hours, it definitely sounds worth resuscitating.

It has enough sentimental value to keep, for now, but I guess I don't see
any real reason to resuscitate it. Emulation on a modern PC would run many
times as fast. I have kept all the paper tape software and the "high-speed"
paper tape reader.

As to the core memory, I lucked out.

The 1620 stack had a two-level scheme to drive the 100 x 100 grid of
selection wires. There were two sets of 100 switch cores that actually
drove the wires in the core stack, one set for each axis. Each of those 200
switch cores was threaded with two wires itself - a total of 20 wires for
each set of 100 switch cores. You put a pulse through the two wires
threaded through a particular switch core to make it flip - thus sending a
pulse on a desired selection wire in the main core stack. You could think
of the switch cores as a decimal decoder. There were ten "10s" wires, and
ten "units" wires threaded through the set of 100 switch cores.
Simultaneously pulse the "70" and the "3" wires to the switch cores and the
"73" selection wire to one axis of the main core stack was pulsed. The
other axis of the main core stack had a similar scheme.

Since I was only implementing 4096 locations, I didn't have to drive all the
"10s" and "units" wires to the switch cores. I had to drive 64 of the 100
switch cores on each axis - and I could use any 64 I wanted. I split the
12-bit address into two 6-bit halves and drove the switch cores with decoded
versions from the 6-bit half associated with that axis of the main memory
stack. The 64 switch cores for each axis only required use of 8 of the
"10s" lines and 8 of the "units" wires through the switch cores for that
axis - a total of 16 drivers per axis or 32 total switch core drivers - far
better than the 128 I would have needed to directly drive the main core
stack selection wires.

The 1620 core stack was thus a little unconventional, but was a big win for
me.

73 de bob w3otc

"Dave, AA6YQ" wrote in message
et...
Getting core memories to work was black magic with the original designers
at
your side; that's something that you got a 1620 stack working on your own.
For the price of a few electrolytics -- or a new switching PS -- and a few
more hours, it definitely sounds worth resuscitating.

It has enough sentimental value to keep, for now, but I guess I don't see
any real reason to resuscitate it. Emulation on a modern PC would run many
times as fast. I have kept all the paper tape software and the "high-speed"
paper tape reader.

As to the core memory, I lucked out.

The 1620 stack had a two-level scheme to drive the 100 x 100 grid of
selection wires. There were two sets of 100 switch cores that actually
drove the wires in the core stack, one set for each axis. Each of those 200
switch cores was threaded with two wires itself - a total of 20 wires for
each set of 100 switch cores. You put a pulse through the two wires
threaded through a particular switch core to make it flip - thus sending a
pulse on a desired selection wire in the main core stack. You could think
of the switch cores as a decimal decoder. There were ten "10s" wires, and
ten "units" wires threaded through the set of 100 switch cores.
Simultaneously pulse the "70" and the "3" wires to the switch cores and the
"73" selection wire to one axis of the main core stack was pulsed. The
other axis of the main core stack had a similar scheme.

Since I was only implementing 4096 locations, I didn't have to drive all the
"10s" and "units" wires to the switch cores. I had to drive 64 of the 100
switch cores on each axis - and I could use any 64 I wanted. I split the
12-bit address into two 6-bit halves and drove the switch cores with decoded
versions from the 6-bit half associated with that axis of the main memory
stack. The 64 switch cores for each axis only required use of 8 of the
"10s" lines and 8 of the "units" wires through the switch cores for that
axis - a total of 16 drivers per axis or 32 total switch core drivers - far
better than the 128 I would have needed to directly drive the main core
stack selection wires.

The 1620 core stack was thus a little unconventional, but was a big win for
me.

73 de bob w3otc

Yes, an emulation would be much faster, but you'd miss those flashing
lights.

Tnx for the core explanation. Data General was still stringing their own
core memory when I arrived in 1972, and there was a fellow who specialized
in designing the read/write circuitry from whom I learned more than I wanted
to know. The last models were 32kbyte arrays on 15" square PCBs. We began
offering RAM-based memory in 1975, using 2K dynamic RAMs built in DG's
Sunnyvale fab; that was the heydey of vertical integration - DG made
everything from TTL to tape drives.

73,

Dave, AA6YQ


"R J Carpenter" wrote in message
...

"Dave, AA6YQ" wrote in message
et...
Getting core memories to work was black magic with the original
designers
at
your side; that's something that you got a 1620 stack working on your
own.
For the price of a few electrolytics -- or a new switching PS -- and a
few
more hours, it definitely sounds worth resuscitating.

It has enough sentimental value to keep, for now, but I guess I don't see
any real reason to resuscitate it. Emulation on a modern PC would run
many
times as fast. I have kept all the paper tape software and the
"high-speed"
paper tape reader.

As to the core memory, I lucked out.

The 1620 stack had a two-level scheme to drive the 100 x 100 grid of
selection wires. There were two sets of 100 switch cores that actually
drove the wires in the core stack, one set for each axis. Each of those
200
switch cores was threaded with two wires itself - a total of 20 wires for
each set of 100 switch cores. You put a pulse through the two wires
threaded through a particular switch core to make it flip - thus sending a
pulse on a desired selection wire in the main core stack. You could think
of the switch cores as a decimal decoder. There were ten "10s" wires, and
ten "units" wires threaded through the set of 100 switch cores.
Simultaneously pulse the "70" and the "3" wires to the switch cores and
the
"73" selection wire to one axis of the main core stack was pulsed. The
other axis of the main core stack had a similar scheme.

Since I was only implementing 4096 locations, I didn't have to drive all
the
"10s" and "units" wires to the switch cores. I had to drive 64 of the 100
switch cores on each axis - and I could use any 64 I wanted. I split the
12-bit address into two 6-bit halves and drove the switch cores with
decoded
versions from the 6-bit half associated with that axis of the main memory
stack. The 64 switch cores for each axis only required use of 8 of the
"10s" lines and 8 of the "units" wires through the switch cores for that
axis - a total of 16 drivers per axis or 32 total switch core drivers -
far
better than the 128 I would have needed to directly drive the main core
stack selection wires.

The 1620 core stack was thus a little unconventional, but was a big win
for
me.

73 de bob w3otc

Yes, an emulation would be much faster, but you'd miss those flashing
lights.

Tnx for the core explanation. Data General was still stringing their own
core memory when I arrived in 1972, and there was a fellow who specialized
in designing the read/write circuitry from whom I learned more than I wanted
to know. The last models were 32kbyte arrays on 15" square PCBs. We began
offering RAM-based memory in 1975, using 2K dynamic RAMs built in DG's
Sunnyvale fab; that was the heydey of vertical integration - DG made
everything from TTL to tape drives.

73,

Dave, AA6YQ


"R J Carpenter" wrote in message
...

"Dave, AA6YQ" wrote in message
et...
Getting core memories to work was black magic with the original
designers
at
your side; that's something that you got a 1620 stack working on your
own.
For the price of a few electrolytics -- or a new switching PS -- and a
few
more hours, it definitely sounds worth resuscitating.

It has enough sentimental value to keep, for now, but I guess I don't see
any real reason to resuscitate it. Emulation on a modern PC would run
many
times as fast. I have kept all the paper tape software and the
"high-speed"
paper tape reader.

As to the core memory, I lucked out.

The 1620 stack had a two-level scheme to drive the 100 x 100 grid of
selection wires. There were two sets of 100 switch cores that actually
drove the wires in the core stack, one set for each axis. Each of those
200
switch cores was threaded with two wires itself - a total of 20 wires for
each set of 100 switch cores. You put a pulse through the two wires
threaded through a particular switch core to make it flip - thus sending a
pulse on a desired selection wire in the main core stack. You could think
of the switch cores as a decimal decoder. There were ten "10s" wires, and
ten "units" wires threaded through the set of 100 switch cores.
Simultaneously pulse the "70" and the "3" wires to the switch cores and
the
"73" selection wire to one axis of the main core stack was pulsed. The
other axis of the main core stack had a similar scheme.

Since I was only implementing 4096 locations, I didn't have to drive all
the
"10s" and "units" wires to the switch cores. I had to drive 64 of the 100
switch cores on each axis - and I could use any 64 I wanted. I split the
12-bit address into two 6-bit halves and drove the switch cores with
decoded
versions from the 6-bit half associated with that axis of the main memory
stack. The 64 switch cores for each axis only required use of 8 of the
"10s" lines and 8 of the "units" wires through the switch cores for that
axis - a total of 16 drivers per axis or 32 total switch core drivers -
far
better than the 128 I would have needed to directly drive the main core
stack selection wires.

The 1620 core stack was thus a little unconventional, but was a big win
for
me.

73 de bob w3otc

Geoffrey G. Rochat wrote:
kenneth scharf wrote in message
...

Does anybody know where I can get a Harris or Intersil
HD6100, HD6120, IM6100, or IM6120 microprocessor (cmos pdp-8)?

I used to work for Digital, and thought it would be an interresting

project

to homebrew a PDP-8 system. I have a T11 microprocessor chip in the

junbox

someplace, so a PDP-11 system is also a possibility.




In fact, there is a fellow who sells kits and parts for the SBC6120, which
is a build-your-own PDP-8 based on the IM6120 chip:

http://www.sparetimegizmos.com/Hardware/SBC6120-2.htm

And this fellow has an add-on for the SBC6120:

http://www.jkearney.com/sbc6120/iob6120.htm

Also, IM6100 chips show up on eBay from time to time.

PDP-8 documentation may be found at Al Kossow's site:

http://www.spies.com/~aek/pdf/dec/pdp8/

And at Dave Gesswein's site:

http://www.pdp8.net

Also, Bob Supnik's SIMH retrocomputing simulator supports the PDP-8. SIMH
is hosted at Tom Shoppa's Trailing Edge site, currently down due to the
effects of Isabel:


Now that's a name I haven't heard for a while. I worked with Bob at DEC
some 25 years ago.
Bob's the nerd that translated the Dungeon (aka Zork) game from Muddle into
Fortran to port it from the PDP-10 to the PDP-11 under RT11