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Standard backplanes with full ground plane?

J

Joerg

Jan 1, 1970
0
For prototyping a large embedded system I am looking for a card rack
with a good backplane. 20 or more slots, 64 or 96 pin DIN connector or
similar, single height, maybe Eurocard-size. Preferably not Press-Fit
but we can always hand solder, of course. Most of what's available is
VME with super-wide power and ground traces but as far as I could make
out from the data sheets no full ground plane. We've got analog stuff on
most of the cards so a ground plane is important. The bottom
(solder-side) layer should be traces so we can cut some for slot ID and
analog stuff, can't use 100% internally bussed versions.

Short of laying out our own (again...), is there something with a ground
plane that can be had off-the-shelf?
 
D

Del Cecchi

Jan 1, 1970
0
Joerg said:
For prototyping a large embedded system I am looking for a card rack
with a good backplane. 20 or more slots, 64 or 96 pin DIN connector or
similar, single height, maybe Eurocard-size. Preferably not Press-Fit
but we can always hand solder, of course. Most of what's available is
VME with super-wide power and ground traces but as far as I could make
out from the data sheets no full ground plane. We've got analog stuff
on most of the cards so a ground plane is important. The bottom
(solder-side) layer should be traces so we can cut some for slot ID and
analog stuff, can't use 100% internally bussed versions.

Short of laying out our own (again...), is there something with a
ground plane that can be had off-the-shelf?
People actually still make backplanes without ground planes in them? You
sure about that?

Try buying maybe one of the backplanes made for blade servers. Gotta be
generic stuff out there.

You can't even do controlled impedence traces without planes.

del
 
J

Joerg

Jan 1, 1970
0
Del said:
People actually still make backplanes without ground planes in them? You
sure about that?

Try buying maybe one of the backplanes made for blade servers. Gotta be
generic stuff out there.

You can't even do controlled impedence traces without planes.

Blade servers, good point. I'll look if they have some that are 20-wide
or more.
 
J

John Larkin

Jan 1, 1970
0
For prototyping a large embedded system I am looking for a card rack
with a good backplane. 20 or more slots, 64 or 96 pin DIN connector or
similar, single height, maybe Eurocard-size. Preferably not Press-Fit
but we can always hand solder, of course. Most of what's available is
VME with super-wide power and ground traces but as far as I could make
out from the data sheets no full ground plane. We've got analog stuff on
most of the cards so a ground plane is important. The bottom
(solder-side) layer should be traces so we can cut some for slot ID and
analog stuff, can't use 100% internally bussed versions.

Short of laying out our own (again...), is there something with a ground
plane that can be had off-the-shelf?

VME backplanes have ground planes, and we do all sorts of analog stuff
in VME. Never had a problem we could blame on a backplane, even using
a motley collection of ebay crates and a bazillion different customer
situations.

http://www.highlandtechnology.com/Pages/prodind2.html#VMEprod

The slot ID thing would be a challenge with 3U VME. No problem in 6U.

John
 
R

Rene Tschaggelar

Jan 1, 1970
0
Del said:
People actually still make backplanes without ground planes in them? You
sure about that?

Try buying maybe one of the backplanes made for blade servers. Gotta be
generic stuff out there.

You can't even do controlled impedence traces without planes.

Actually you can. "Coplanar transmission line" is the word.
A 5mil gap to either side and you get an impedance.

Rene
 
R

Rene Tschaggelar

Jan 1, 1970
0
Joerg said:
For prototyping a large embedded system I am looking for a card rack
with a good backplane. 20 or more slots, 64 or 96 pin DIN connector or
similar, single height, maybe Eurocard-size. Preferably not Press-Fit
but we can always hand solder, of course. Most of what's available is
VME with super-wide power and ground traces but as far as I could make
out from the data sheets no full ground plane. We've got analog stuff on
most of the cards so a ground plane is important. The bottom
(solder-side) layer should be traces so we can cut some for slot ID and
analog stuff, can't use 100% internally bussed versions.

Short of laying out our own (again...), is there something with a ground
plane that can be had off-the-shelf?

Joerg,
I suggest making your own. Standard backplanes have
standard distances. Even the worst autorouter can't do
anything wrong.

Rene
 
J

Joerg

Jan 1, 1970
0
John said:
VME backplanes have ground planes, and we do all sorts of analog stuff
in VME. Never had a problem we could blame on a backplane, even using
a motley collection of ebay crates and a bazillion different customer
situations.

Yes, meantime I found some with planes. But all traces inside, can't
unhook some of the DIN pins without major surgery. I guess we'll roll
our own again then.


Nice! Interesting that you guys tend not to use the 2nd rail.

The slot ID thing would be a challenge with 3U VME. No problem in 6U.

6U is too monstrous for this case. It's not just ID we need but also
some near-realtime signaling from the boards to a host where the usual
IRQ1 arbitration would take too long.

Question: Since you don't seem to use slot ID how do identical boards in
one rack know which position they are in? DIP switches? Or maybe they
don't have to know in your cases?
 
J

Joerg

Jan 1, 1970
0
Rene said:
Joerg,
I suggest making your own. Standard backplanes have
standard distances. Even the worst autorouter can't do
anything wrong.

We probably will. There comes a point where it's more economical to just
whip up a board rather than searching for hours. I just hope that my
layouter has a VME template with all the connector positions and holes
on his CAD. Then it would be really easy. Another thing I had done
before is just solder one by hand. No big deal if the iron has 100W+ but
the stench from that activity was quite nasty.
 
D

Del Cecchi

Jan 1, 1970
0
Rene said:
Actually you can. "Coplanar transmission line" is the word.
A 5mil gap to either side and you get an impedance.

Rene
not very controlled unless you have control of above and below. And via
locations.
 
J

Joerg

Jan 1, 1970
0
Del said:
not very controlled unless you have control of above and below. And via
locations.

During my search I came across quite a few of these. Mostly called
"Faraday shielded", guess because the marketeers thought that sounds
more fancy. They also staggered the lines so they are offset to each
other between planes. Well, to some extent. It might be a bit of a
white-knuckle ride on a 21-slot board.
 
J

John Larkin

Jan 1, 1970
0
Yes, meantime I found some with planes. But all traces inside, can't
unhook some of the DIN pins without major surgery. I guess we'll roll
our own again then.

I wonder how many backplanes have been invented over the years. I've
done a few myself.

Nice! Interesting that you guys tend not to use the 2nd rail.

The analog stuff is mostly slow, so we don't really need 32 bit
transfers. Leaves more room on the board for stuff!
6U is too monstrous for this case. It's not just ID we need but also
some near-realtime signaling from the boards to a host where the usual
IRQ1 arbitration would take too long.

Doesn't CPCI have geographic addressing? Those backplanes are mass
produced, too.
Question: Since you don't seem to use slot ID how do identical boards in
one rack know which position they are in? DIP switches? Or maybe they
don't have to know in your cases?

Dip switches. Nobody seems to mind.

John
 
J

John Larkin

Jan 1, 1970
0
We probably will. There comes a point where it's more economical to just
whip up a board rather than searching for hours. I just hope that my
layouter has a VME template with all the connector positions and holes
on his CAD. Then it would be really easy. Another thing I had done
before is just solder one by hand. No big deal if the iron has 100W+ but
the stench from that activity was quite nasty.

We have the basic VME board layouts, in PADS, if that would help.

John
 
J

Joerg

Jan 1, 1970
0
John said:
I wonder how many backplanes have been invented over the years. I've
done a few myself.

In ultrasound we ended up making our own. Every single time. Lack of
slot ID was just one reason, there just weren't enough configurable
lines, or in cases like VME there were none at all.
The analog stuff is mostly slow, so we don't really need 32 bit
transfers. Leaves more room on the board for stuff!




Doesn't CPCI have geographic addressing? Those backplanes are mass
produced, too.

But they are overkill with their 220 pin connectors and you can usually
only get them with 8 slots. Plus they are, gasp, metric ;-)
Dip switches. Nobody seems to mind.

In this case that is bound to cause trouble because there will be dozens
of boards that are going to be swapped a lot. DIP switches are also not
reliable IMHO. When using the ADN8831 eval board for a TEC controller I
was almost done tuning the PID when one broke off. Luckily someone had a
sewing needle so I could move that position one more time.
 
J

Joerg

Jan 1, 1970
0
John said:
We have the basic VME board layouts, in PADS, if that would help.

Thanks, it might help since my layouter also uses PADS. He just told me
that he has done customized VME-type backplanes and has the important
outlines etc. but that the dimensions are different between rack
manufacturers. Meaning one VME backplane may not fit into the rack of
another vendor. Oh man, did they screw up that standard as well?
 
J

joseph2k

Jan 1, 1970
0
Joerg said:
Yes, meantime I found some with planes. But all traces inside, can't
unhook some of the DIN pins without major surgery. I guess we'll roll
our own again then.



Nice! Interesting that you guys tend not to use the 2nd rail.



6U is too monstrous for this case. It's not just ID we need but also
some near-realtime signaling from the boards to a host where the usual
IRQ1 arbitration would take too long.

Question: Since you don't seem to use slot ID how do identical boards in
one rack know which position they are in? DIP switches? Or maybe they
don't have to know in your cases?

The more i read, the more it seems, that what you want is VXI bus instead.
 
J

Joerg

Jan 1, 1970
0
joseph2k said:
Joerg wrote:




The more i read, the more it seems, that what you want is VXI bus instead.

Well, for the protoype my client got a hold of old-style VME via EBay.
After that we'll lay out our own anyway because a typical bus backplanes
is prohibitively expensive. The old ones have bottom and top traces so
we can cut and wire for a prototype system. So we'll have automatic slot
detection from day one :)
 
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