We've currently got a SCADA system product that I'm pretty happy with in=20
general.  After being in the field for a year or so, though... it's=20
beginning to show one obvious area for improvement.  I'd like to switch=20
to an easier to use and more capable backplane.

It's a modular system.  Currently, the PCBs are sandwiched together (CPU=20
on top, "backplane", then expansion boards).  Power supplies are mounted=20
nearby, and the system is wired up to an access panel for installers to=20
hook up to easily.  The current "bus" is simply SPI with encoded chip=20
selects.  The current data transfer needs across the backplane are=20
pretty low...  500kB/sec max.

We've got a few issues with this:

1) In practice, the system integrators who use the system aren't=20
comfortable with pulling the boards out to install expansions or=20
reconfigure units.
2) We'd like to reduce our assembly time per unit by reducing the need=20
for power supply wiring, etc.
3) We want to add some redundancy and possibly hot-plugging if=20
reasonably possible.

I thought about my requirements for a bit and the easy solution in my=20
mind is to have a simple card-edge backplane with vertical slots using=20
different length fingers for hot plugging.  I could have two CPU slots,=20
two power supply slots, and some expansion card slots. Some expansion=20
cards have non-trivial heat loads (and there's no ventilation at all),=20
so I need to be able to screw heat sink plates on expansion modules down=20
to the main chassis directly.

....

However, I feel like I'm re-solving a very old problem... and my=20
solution is right out of the 1980s.  Perhaps I should use a more modern=20
backplane design.

The main constraint is the CPU.  It's a Freescale i.MX28x series=20
processor.  It's more targeted for mobile phones than embedded=20
systems... there's not really a good general purpose high bandwidth=20
interface to external devices.  So, I'm using SPI bus.  I don't want to=20
replace the CPU this time around.  I -could- put an FPGA on the CPU=20
board to translate to the system bus until I replace the CPU with=20
something else down the road.


Any suggestions?


Darron Black

--=20
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