Spec issue on MSE leakage current in SPI-3

Daniel_F_Smith at notes.seagate.com Daniel_F_Smith at notes.seagate.com
Fri Apr 30 08:48:11 PDT 1999

* From the T10 Reflector (t10 at symbios.com), posted by:
* Daniel_F_Smith at notes.seagate.com
Okay, 55 ohms. I forgot about 2 terminators on the bus.  That makes passive
negation capable of 100mA if an active terminator goes astray. And yes, it
is an issue with terminators as well as drivers.  I would think that most
drivers turn off their current sourcing as they approach passive negation
levels to save power and minimize ringing.  But you are right, if a driver
actively negates, strongly, we're looking at a lot of potential current.
The real question is: can the bus survive this type of activity without
loss of data?  I don't have any data on this, does anyone else have
experience that they can share?  Let's try to refrain from throwing rocks
and see if we can prove this either way.

Bill:  What is our exposure to passively negated, legacy devices, today?
Would many of these end up on a multimode bus?

* From the T10 Reflector (t10 at symbios.com), posted by:
* "Bill Galloway" <BillG at breatech.com>

Actually the resistance is 55 ohms not 110 as far as DC is concerned. I do
think the spec needs to fix broken terminators so I think we can ignore a
passively negated bus.  The only issue I have is with an actively negated
In this case the terminators are probably not supplying any current, only
negation driver. This driver could put out a lot of current at 4.0V.

I think that there are two strong and opposing forces at work here. On one
are the suppliers of silicon that have a very hard time meeting these specs
say that they need relief. On the other side are the systems vendors that
do not
want to deal with customers that are upset because previous generation
were outlawed. It goes against promises of investment protection.

If we are really going to outlaw previous generation devices we might as
get rid of all that cumbersome negotiation too. ;-) (I just heard a big
|from the gallery.)

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