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RE: Self-mastering?



Shawn,

I mostly agree with you.  However, where you wrote:

>- PCI 2.1 seems to disallow source terminated transmission lines ...

Actually, PCI 2.1 does use source termination.  It is part of what makes
reflected wave switching work.  The source termination is internal to
the driving device, by way of its V/I curves which effectively define a
range of source impedances for the driver.  There is no external source
termination resistor.

>  I'm also not
>  quite sure if on a bi-directional bus, a source termination
>  qualifies as an "unterminated end".

"Unterminated end" means there are no parallel terminations on the ends
of the bus.  Source termination can co-exist with that, and usually
does.  Even if there are source-terminated devices on the "unterminated"
ends of the bus.  It's not the best terminology.

However, the implied difference between 2.1 and 2.2, about whether Tprop
includes a driver to itself, is rather puzzling.  The other sections you
quoted from 2.1, are still there in 2.2, which makes it even more
confusing.

Regards,
Andy Ingraham