Re: [Xylo-SDR] Fundamental Atlas design decisions

["Ray Anderson" <ray.anderson@xilinx.com>]

Phil C wrote:


>I think the quantity 4 plug-in boards for the Atlas was originally the
>result looking at using an extruded case that we then dropped.   We
>also had discussions of using the Aria case (which has 4 PCI slots on
>the back).  I am not sure that four slots will be enough.  I would
>like to see 6.  I am at work so I can't look at my Aria case - I am
>not sure if there is room for a backplane with 6 slots - Can someone
>check this?  The spacing of the boards was dictated by the PCI card
>spacing.  If people are not going to use the Aria case then there is
>no point letting it dictate the quantity of plug-in boards per
>backplane. I also think that if we has 6 slots on the backplane we
>could then drop the idea of expansion connectors on the backplane. 
>For special cases the plug-in boards could have a daughterboard header
>allowing expansion as needed and special functions.

	I think the concept of designing in more than 4 slots (i.e. 6 or
whatever) to provide flexibility for adding more boards is the way to
go as opposed to planning on buss extender boards. When we provide
LVDS termination on the backplane it is important to minimize the
parasitics. If bus extenders are part of the plan then the
termination on the mother board will need to be deactivated when the
extenders are used. This implies the use of either plug in terminators,
header shorting blocks or something similar. All of these will 	increase
the parasitic inductance associated with the terminator and 	lead to
increased ringing and other non-desirable artifacts. 


	Question:

	If the DSP board proposed by Lyle were to be used is it
envisioned 	that it would be sitting on the LVDS buss? If so would
it be listen 	only or would it drive the buss at times ??


-Ray	WB6TPU