Classic Computers vs. Classic Computing

From: Douglas Quebbeman <dhquebbeman_at_theestopinalgroup.com>
Date: Fri Sep 14 17:14:20 2001

> On the real machine you can solder up a few TTL chips, wire them to the
> bus connector and add another peripheral. You can't easilly do that on an
> emulator. Or you can solder wires onto the chips on the CPU board of a
> mini, clip a logic analyser to them, and watch the data flow through the
> ALU and registers.
>
> Yes, you can do _similar_ things with emulators, but not quite the same.
> No flames intended, but I'll stick to the real machines ;-)

BTW, if it wasn't implicit (it is to me), I wouldn't have much of a need
for an emulator for a machine that's readily available, or if rare, easy
on the pocketbook to keep running (parts, electricity, etc).

We can't all be Megan Gentry, Eric Smith, or Daniel Seagraves (owners
of DEC-10&20s who come immediately to mind)...

Now, Jim Battle's doing a SOL emulator. Great idea, I might want to
play with a SOL at work. But my SOL was the machine I did exactly the
kinds of things you describe. Unlike many, I didn't buy even the complete
SOL kit. I bought only the motherboard and a folder of schematics and
instructions for component assembly. By December 1976, all it could do
was display a test pattern consisting of essentially a dump of the
character generator ROM. As time went by, I continued buying components.

It was getting close to being finished, but I needed a keyboard. I bought
one surplus, taken from a TI Silent 700. However, the strobe was inverted
and either too long or too short (can't recall). So I fingered through
Don Lancaster's TTL Cookbook until I came across the 74121, which I hadn't
used yet. I used it to change the strobe width, and one gate in a NAND
wired as an inverter to flip the logic direction.

Next, I needed some kind of key-repeat. Like many early terminals,
there was no auto-repeat, but instead, the keyboard included a
REPEAT key. A couple of 555s and some more gates from the NAND,
and I was almost done. I ended up adding a lightpen interface to
the design, then built it up permanently using a Rat Shack proto
board. Stuck that inside a generic keyboard enclosure along with
the TI keyboard, and I could now talk to my SOL.

For a monitor, I followed Lancaster's instructions on how to take
an old B&W TV set and pull the unneeded circuitry (except for the
tubes; they stayed in, heaters wired in series). The mods all helped
boost the bandwidth of the monitor a bit. The image quality ended
up being quite good, and I sold it to another guy who'd bought a
complete SOL kit sans monitor (I'd bought an actual monitor by
this time).

I enjoyed every minute of the 18 months it took me to make that
forty-dollar naked PC board into a usable computer. Or termninal,
actually... its raison d'etre was to hook up to my beloved and
much missed CDC 6600 & DEC-10!

And I think I even got to like the smell of solder.. especially
the Ersin Multicore stuff made in the U.K... why, there's some
now, and no iron in sight...

But as much as I enjoyed fooling with hardware, the software had
an even stronger draw. Just as you can only erase a piece of
paper so many times before it disintegrates, you can only re-
solder a PC board so many times before you've fried it. And
yes, I've used all kinds of techniques to repair such damage.

But you can't damage software... which is one of the things that
I find attractive about it. Emulators represent the ultimate
convergence of hardware and software...

Hey, I just had an idea... how about an emulator that goes all
the way down to the component level? One which actually emulates
resisters, capacitors, transistors, and 7400-series chips. It
could also have an emulated soldering iron & solder. Ever wish
you had three hands for a difficult assembly? No problem in this
proposed emulator! We'll just add an emulated hand... or two... or...

;-)

-dq
Received on Fri Sep 14 2001 - 17:14:20 BST