On 8/30/2024 7:25 PM, cz via cctalk wrote:
To try and turn this thread around: I'm looking to make an extended
memory controller for my pdp8/L. I've got a wire wrap backplane and
enough cards to make it work but I've never done wire-wrap on this sort
of scale.
I've got an old Radio Shack Wire wrap tool and a lot of wire. Is there
any sites that discuss how to do reasonable wire-wrapping?
Some of the older (single-sided especially) DEC back-planes were wrapped
with heavier gauge wire, which needs a different tool. The newer
back-planes seem to be wrapped with 30 gauge wire. You can tell the old
connector blocks, as the pins appear rectangular, rather then square.
There are all kinds of opportunity for optimizing routing for distance,
cross-talk and and other esoterica. One thing that's worth doing,
though, is to wrap for a max height of two, and such that all the
connections (except possibly the last end of a given signal) are at the
same height. So, if A B C and D are to be connected together, you
connect A to B, then C to D (thus all at the lower level), then put the
connection of B to C at a higher level. This dramatically cuts down on
the amount you have to *unwrap* to fix something. Avoid situations which
cross the height boundary, because then you have to keep unwrapping
stuff you'd rather not, to expose the buried lower side.
If you are wrapping by hand, you can be assured that you *will* make
mistakes and have to fix something.
I predict you will also find that you are really sick of wire-wrap long
before you are done. These days, PCBs are inexpensive, and less error
prone (in the sense that you almost always end up with exactly the
connections in the netlist). OTOH, connectors are expensive and hard to
reuse when soldered to a PCB. So you've got to be really confident of
your netlist.
You might consider investing in a tool where you pull the trigger to do
the wrap. You'll probably get a more consistent result, and
significantly fewer repetitive motion issues.
Hope that helps!
Vince
