13 Aug
2006
13 Aug
'06
10:15 p.m.
On 8/14/06, vrs <vrs at msn.com> wrote:
Sure... but the front panel (in this case) doesn't have anything to do
with the size of the CPU board. In the case of the -8/S, the lights
panel is one board (and plugs into the second row) and the switch
panel is another board (and plugs into the first row).
Has anyone
estimated the physical size?
I'd guess something like 1/4 scale would be acheivable. If you make it
too small, you'll have trouble with the user interface (as you mentioned
about the 1/12th scale IMSAI). I'd start out by building replacements for the
Rxxx and Sxxx modules, all
scaled down. (Once a few of those work, you could start in on a backplane
for them.)
Would it be worth the expense of a backplane? I would have thought
that the way to do it would be to lay it out on both sides of single,
largish PCB with off-board connections for I/O and front panel.
I was thinking of a 9x2 header/socket arrangement for
the interconnect
and soldering the header to pads on each side of the board to make little
1" wide modules.
While the originals R and S modules were 18-pin, I'd think that 20-pin
headers, etc, would be easier to find in quantity (not that they
couldn't be trimmed down, of course).
(Were there double-sided Rxxx or Sxxx modules? I
don't
think so, because the connector blocks used to be one sided.)
No. The module blocks were single-sided only.
For testing, you just need a standard size module with
a female 9x2 right
angle connector on it, and insert the miniature card being tested. Replace
an original module in some old gear with the result, to see if you've got
things right. You could also use the technology to resurrect old gear with
missing modules :-).
That's certainly true, but in some cases, they hand-picked modules to
get the timing right.
Another goofy idea I had (for inexpensive
interconnect) was to try to
squeeze
the SMT modules down into the footprint of, say, an 18 or 20 pin DIP. It
wouldn't look much like a replica anymore, though.
I would think the point would be a work-alike replica more than a
board-for-board form-factor-in-miniature replica, but whatever works.
One thing that would help for size is that about 20% of the backplane
size (40x4? 44x4?) is for the 4K core stack. Obviously, that would
end up being a couple of 6264s or something like it, and take up
*substantially* less space than the original. The front 3 rows (a bit
under 10%) or so are the front panel and lamp drivers, and the back
few rows are I/O drivers and cable attachments (10%? 15%?) That
leaves a bit over 50% for the CPU itself, or about 100 R and S
modules, as a rough estimate. I would think that the individual PCB
costs, even for something about 2 sq in., and the interconnect
hardware would start to make this a rather expensive project. It
would, of course, be easier to _test_ dozens of individual modules
than a monolithic CPU PCB (since there wouldn't be any interaction
issues), but quite a bit pricier. OTOH, even with a $1000 budget,
it's cheaper than the going rate for a PDP-8/S these days.
-ethan