Re: Some questions

[cary@agora.rdrop.com (David Cary)]

>>       Can I put in the PCI bus eight cards ? this question is because I'll
>>       build the PCI bus on my project.
>
>Not without violating these specs.  You could have 8 onboard PCI devices (9 if
>you don't need the PCI->ISA bridge).  Or you could use a PCI->PCI bridge to add
>more slots.

Actually, you can get 6 slots (on the same bus, i.e. without bridges)
without violating the CompactPCI spec. (Apparently because the
higher-quality connectors act as somewhat *less* than the 2 loads that the
lower-quality standard connectors act like).

Allow me to quote from a (probably obsolete) document I found:

"Because of its high clock rates PCI is currently limited to 10 loads on
one PCI
bus.  In the desktop world each chip is a load and each connector is one load,
thus limiting the number of PCI slots to three or four (depending on the number
of PCI peripherals on the mother board).  By using a higher grade connector and
increasing the ground/signal ration, it is hoped to reduce the loading of the
connector and support more slots, with six being the design goal.  More slots
will be attainable by the use of emerging bridge chips.
...
CompactPCI is a new specification ... It builds on the proven and widely
available mechanical standard of the Eurorack and the Telecom background of the
IEC-1076 connector technology to create a solid basis for customers and vendors
alike to design to.  The final specification is expected to be voted on by the
PICMG by June of 1995."


<a href="mailto:d.cary@ieee.org">David Cary</a> <*> O-
<a href="http://www.rdrop.com/~cary/">Future Technology</a>.

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