Motherboards are limited to 8
slots. New motherboards only provide PCI slots and do not
allow for ISA cards. System repair or upgrade with a motherboard
installed requires full system disassembly to access the
motherboard.
Chassis Plans Passive and Active
Backplanes allow for more than 8 slots (up to 20), a large
mix of ISA and PCI 
slots,
and easy processor card access. For full PC functionality
with the benefit of increased I/O expandability, Chassis
Plans' full line of ISA and PCI backplanes are the perfect
solution. Available in 4 to 20-Slot options, from ISA to
PCI-X PICMG Bus and Passive to Segmentable systems, these
unique backplanes combine with Chassis Plans' complete line
of Single Board Computers
and Industrial Chassis
products to create a rugged, reliable platform for hostile
operating environments. Chassis Plans passive backplanes
are widely used in industries that require I/O expandability,
including telecom, instrumentation and process control.
Because of all the different
variations in backplanes that can be configured, please
call us at 858-571-4330 or
e-mail us to discuss your requirement.
Please see the Backplane Primer
at the bottom of this page if you have questions about passive
backplane useage.
If you are unfamiliar with passive backplanes, this short
primer should offer some clarification.
Why Use a Passive Backplane?
Why would you use a passive backplane and Single Board
Computer? The three primary reasons are more expansion slots,
need for ISA slots, and much lower MTTR (Mean Time To Repair).
Motherboards are limited to 8 slots maximum - at the most.
It's getting hard to find even that many. Passive Backplanes
can provide up to 20 slots. 20 is the most that will fit
within a 17" wide rack mount chassis. You can build
a backplane with more than 20 if your chassis is wide enough
to accommodate the board.
Intel and Microsoft decreed some time ago that ISA slots
will no longer be supported. New motherboards only provide
PCI slots. If you have an application that is served by
a plug-in I/O which is only available in ISA form factor,
you are limited to looking for used or old stock motherboards
or switching to a passive backplane. A passive backplane
can provide up to 20 ISA slots. However, 1 or 2 of those
slots would be occupied by the SBC leaving 18 available
ISA card slots.
An SBC can be removed from the system by unplugging the
cables, removing one screw, and pulling the card. None of
the I/O cards need to be removed. A motherboard is buried
under everything else requiring a total system deintegration
(disintegration?) to remove the motherboard. All I/O cards
have to be removed and all the screws holding the motherboard
removed. If your application requires low MTTR, the only
option is a total system replacement if you have a motherboard
installed, or use an SBC installed in a passive backplane.
A fourth reason would be continued availability of a stable
design. Motherboards are consumer commodity items with limited
availability. There is no guarantee how long you will be
able to continue to source a motherboard. Single Board Computers
and Passive Backplanes have much longer product life cycles.
For example, in the medical field, FDA approval is expensive.
Every time you change a component such as the motherboard,
you have to resubmit for approval.
The one negative regarding a passive backplane and SBC
is cost. Motherboards are made by the gazillion and are
very cheap. Passive backplanes and SBCs are made in much
smaller quantities and cost considerably more than a motherboard.
Structure
A Passive Backplane provides the slots, but not the smarts
of a motherboard. Various motherboards provide for 1 to
8 I/O card expansion slots. The motherboard also provides
the processor, processor support chip sets, memory, I/O,
etc. A passive backplane needs the smarts provided by a
plug-in Single Board Computer (SBC) to function. A passive
backplane with an SBC installed it totally equivalent to
a motherboard.
As with motherboards, passive backplanes provide a mix
of I/O slots. These can be all ISA, a combination of ISA
and PCI, or all PCI. Because of signal loading requirements,
backplanes with PCI slots will also provide bridge chips.
So, in the true sense of the word, these are not "passive"
backplanes, but "active". For simplicity, they
are all grouped as "passive" backplanes.
Single Board Computers can be selected with a wide variety
of features including processor type and speed, available
memory, video, I/O, etc. With regards to a passive backplane,
the only concern will be the connection between the SBC
and the backplane. An SBC looks like any other plug-in card.
Hanging from the bottom will be an ISA connector and maybe
a PCI and PICMG
connectors if the board supports PCI. Note that a PCI SBC
will work in an all ISA slot backplane. An ISA-only SBC
will work in an ISA/PCI backplane but will not provide any
PCI support (PCI slots will not be active). The ISA signals
are carried on the ISA edge connectors and the PCI signals
are carried and controlled by the PICMG edge connectors.
An ISA-only backplane can have the SBC installed in any
slot. A PCI backplane will provide dedicated SBC slot(s)
and the SBC must be installed in one of these for the system
to work.
Segmented Backplanes
Segmented or split backplanes provide for multiple independent
SBCs 
to
be used in the same backplane. Each SBC has a group of slots
dedicated to it. Only power and mechanical support are shared.
In theory (and practice), a 20-slot backplane could be split
into 10 segments allowing 10 SBCs and 10 I/O cards to be
installed in a single 4U chassis. Because the SBCs share
power, each SBC cannot be individually turned on/off. However,
each SBC can be provided with its own reset switch. Imagine
the processing power available with ten 3GHz dual-Xeon SBC's
in a single 4U enclosure!
Custom Backplanes
As with our Custom Chassis, Chassis Plans can provide you
with custom backplanes with any slot 
mix,
any number of segments or special mechanical features. It
is possible to add circuitry to the backplane to provide
functionality not available in a plug-in card or to conserve
I/O slots. There is a 50 piece minimum order for custom
backplanes and NRE charges will apply. We have over 30 custom
designs available with no NRE charges applicable. Contact
the Chassis Plans sales department with your custom requirements
for a quotation.
