Re: DIN 41612 backplane?

[lynchaj <lyn...@yahoo.com>]

On Jun 24, 5:14 pm, jdavis <soupw...@gmail.com> wrote:
> On Jun 23, 7:04 pm, Seth Morabito <smor...@gmail.com> wrote:
>
> > Does anyone know where to find inexpensive, ready-made passive VME
> > backplanes?  I've been looking everywhere, but I seem to be failing.
>
> Are you thinking about using that with the n8vem board?  I don't know
> anything about busses, but if you could find a prebuilt passive
> backplane semi-cheap, that would be cool.   Maybe you'd need a custom
> "terminator" board to make it work with the n8vem bus, I don't know.
>
> Jeff

Hi Seth, Thanks!  Excellent question and I much appreciate you
bringing up the topic!

I don't know about the ready made passive VME backplanes.  Maybe they
would work with the N8VEM, I do not know.  The first thing I would
check is to see if the pinouts are compatible with ECB.  On ECB the
Vcc and Gnd pins are the outermost pins.  The rest are control, data,
address, other, and unassigned.

However, from my work experience I normally do not associate cheap and
VME together.  They tend to be industrial and/or military grade items
which are quite expensive items.  Serious $$$!  I suppose hobbyist
grade VME exists somewhere but I haven't seen it.  Maybe in the
surplus market?  If we could find some and they work, it would be a
MAJOR leap in progress that will save the project weeks or months of
development time.

Since the N8VEM uses ECB you might be able to get an ECB backplane or
used one for reasonable amounts.  I certainly would be interested if
you find some.  Here is a link for a company in Germany but they don't
look particularily inexpensive.

http://www.hartmann-elektronik.de/en/products/standard/ecbbus_3u/

Possibly an STE backplane may work as well since it uses the same
connector.  I am not sure about the pinout though.  The pinout is
important for the current carrying Vcc and Gnd lines.

If you can wait a while, the next N8VEM project is the matching ECB
backplane.  I have the schematic and PCB layout on the website in the
ZIP file.  As soon as I get a chance I have to make some updates and
then will repost the data for some review.

The ECB backplane design only six slots and very small (Eurocard
format 160x100mm) but provide power, ground, switching, and power
indicator.  It is unterminated because the PCB traces are small length
and connectors few and operating frequency (4MHz) is fairly low.  It
should be enough for a hobbyist bus assuming all the peripheral cards
are buffered.  The primary goal being to make something useful but
also inexpensive.  The PCB would be $20 a piece just like the SBC.

Although the ECB backplane is next, really it is incomplete without
the ECB bus debugger card.  That is the following N8VEM project.  I
have one on my workbench I made with prototype boards.  It is pretty
crude but using a bus for development without one is pretty
difficult.  It works but I have improvements planned for single step
mode, buffering the inputs, manufactured PCB, etc.

In short, there are other peripherals planned for the project but
we've got a pretty big hump to climb over in the meantime.  First, we
need to get the first generation adopters (you wonderful and brave
folks!) up and running.  Other than you (Seth) and me, I know of one
other person with a working N8VEM SBC.

I assume some percentage will be satisfied with just the SBC and that
will be it for them.  However, some would have also expressed interest
in expansion peripherals and that requires the bus and bus requires
the debugger, etc.

The only real expansion peripheral I have right now is the Disk IO
board.  Again, it is only a prototype on my bench.  It is real and
works.  The CBIOS supports its IDE interface in CP/M as the C:, D:,
and E: drives.  I know the C: drive works but D: and E: are not
complete yet.  The Disk IO board also includes a built but not fully
tested FDC based on the NEC765 using an FDC9229 data separator.  That
is a whole other story we'll save for another day though.

Thanks and have a nice day!

Andrew Lynch