two loads on a single connector ?

[fmnemeth@collins.rockwell.com]

The biggest thing i would pay attention to is the motherboard, and the
topology of the PCI bus you desire. If you place your dual-PCI-Agent board
at one end of the PCI bus (make sure it is really the end, and there are no
chips off the end of the bus, on the motherboard!), the two parts look like
an extension to the bus rather than two clustered loads in the middle of
the bus. PCI may be more well-behaved that way. In addition, if you were to
so constrain this, it would not really be necessary to pay attention to
trace length constraints to one of the Agents, since you would be adding to
the total bus length, not introducing a stub. In addition you would be best
to lay out your board so that there are no tees in the PCI routing; each
PCI line runs in a daisy-chain from the connector, to one PCI Agent, then
directly to the other PCI Agent (which could be centimeters away).

Granted that this is not ideal (a note for the purists out there....), but
i feel it stands the greatest likelihood of working.

mike nemeth

--------------------------------------
The above are opinions of the author, and not necessarily those of Rockwell
Collins, Inc.
--------------------------------------

----- Forwarded by Frank M Nemeth/CedarRapids/Collins/Rockwell on 07/18/00
08:42 AM -----
                                                                                                
                      "Muzaffer                                                                 
                        Kal"             To:     pci-sig@znyx.com                               
                    <muzaffer@kal        cc:                                                    
                    .st> (by way         Subject:     two loads on a single connector ?         
                      of Daniel                                                                 
                    Weaver <danw                                                                
                                                                                                
                      07/17/00                                                                  
                      04:03 PM                                                                  
                                                                                                
                                                                                                





The question I have is whether I can use two loads on a single board.
This board will run only in a controlled environment and will be the
only board (at most one other) in a 4 slot PC motherboard. The problem
is that I need to talk to one chip which has a PCI connection and a CPU
connection. I need to connect an FPGA to the CPU bus of the chip and the
FPGA has to reside on PCI too. I don't want to design two boards and use
a ribbon cable to do the connection. What should I pay attention to in
a system like this ? I am thinking about putting the two PCI chips on
different sides of the board ? This should let me meet the trace length
constraints. Is this a viable solution ? Again this board will exist in
a controlled environment where not all the slots will be filled.

Muzaffer Kal