8 Mar
2009
8 Mar
'09
11:57 a.m.
Hi Andrew,
Before you commit you may want to consider bus termination
for the data/address/control lines. One area a troubles can
s100 to host bridge grounding and signals. You really want
the N8VEM and you S100 to ahve excellent grounds between them.
Also since your using Z80 S100 spec is that a8-15 are an echo
of A0-A7 during IO operations. Not all S100 Z80's did that but
many did and some fo the older IO boards expected that as it
allowed easier routing for the board. You may have to have bus
timing issues as ALL Z80 baords had to bend the Z80 timing to
S100 timing. I assume the bridge baord will do that.
Beware, no matter how well you design due the variables and
ages of some boards you will have boards that refuse to
behave. It's a side effect of early 8080 S100 and later
Z80 S100 and then finally IEEE696 and the subtle differnces
that evolved.
Allison
Subject: RE: S-100 backplane board spacing
From: "Andrew Lynch" <lynchaj at yahoo.com>
Date: Sat, 07 Mar 2009 10:43:54 -0500
To: <cctalk at classiccmp.org>
S-100 backplane board spacing
Hi, here is a rough draft of the PCB layout for a low cost S-100 prototyping
PCB I am considering.? The primary goal is to make this PCB affordable yet
still useful to S-100 hobbyists.? It is not intended to be a full blown
S-100 system or a permanent backplane but rather a bench tool.? Keeping the
costs low means a small number of connectors and?avoiding features such as
termination, etc.???Having a small number of connectors minimizes the bus
length and reduces the need for termination.? A benefit of this backplane is
a hobbyist could use it to develop new boards and/or repair older ones
without risking damage to a costly or rare vintage S-100 chassis.
?
The builder would have to supply the necessary S-100 voltages from their own
power supply.? The power supply interface is just PCB pads that could have a
connector or just direct wired to the supply.? Possible power supply
solutions would be off the shelf SMPSUs to supply +15VDC, -15VDC, and 9VDC
to the rails or alternatively surplus laptop adapters could be modified to
supply the necessary power.? A small number of boards reduces the need for
large power supply capacity.
?
The 13x2 dual row header connectors are optional for use as a stand alone
S-100 backplane.? However, they are necessary for my own project which will
use?this PCB.? PCB construction will be the usual double thickness PCB for
rigidity and double weight traces for current capacity.
?
http://n8vem-sbc.pbwiki.com/f/Printing%20S100-Backplane-full-brd.pdf
?
If you would be interested in a PCB, please contact me off list.? My intent
is to keep this consistent with the other N8VEM PCBs so the target price is
$20 each for the PCB only plus shipping.? There is no estimate for arrival
for the PCB as of now.? I am only trying to gauge what, if any, interest
there might be in the S-100 hobbyist community.
?
Constructive comments, suggestions, and questions appreciated.? Thanks and
have a nice day!
Andrew Lynch