Tom,
Thanks for your answers. So according to this, it is perfectly
legal to have package (and even on-die interconnect) traces
in BIRD189 style go to NC pins or pads... The interesting thing
about this is going to be the buffer terminal end of an NC pin
trace, since NC is in the place of the model name in the [Pin]
keyword, and as a result, by definition, we can't have a [Model]
behind an NC pin in IBIS...
Should any of this be mentioned in BIRD189?
Thanks,
Arpad
=================================================
From: Tom Dagostino [mailto:tom@xxxxxxxxxxxxxxxxx]
Sent: Friday, July 21, 2017 11:52 AM
To: Muranyi, Arpad <Arpad_Muranyi@xxxxxxxxxx>; 'IBIS-ATM'
<ibis-macro@xxxxxxxxxxxxx>; 'IBIS-Interconnect' <ibis-interconn@xxxxxxxxxxxxx>
Subject: RE: [ibis-macro] BIRD189 and NC pins
Arpad
NC pins can be of three varieties.
The first is a pin on a package that has no connection to the die. Depending on
the package style there may be a path from the outside of the package to a
bonding die pad, a TSSOP would be like this. A BGA may just have a ball with
no internal trace. With these pins the user can connect the pin to power,
ground or not to anything. In some cases to ease layout (but can cause stubs)
a trace may be connected to this pin.
The second NC is a pin that is connected to the die but is not to be connected
to anything in the outside world. These pins are used by the IC vendor for
testing. They usually have a weak pullup or pulldown to fix the pin in the
correct logic state.
The third kind of NC must be tied to power or ground. These pins are usually
used by the vendor for testing purposes but don't have the internal pullup or
pulldown for some reason.
So you need to read and understand the datasheet. There is no rule based on
the pins' name.
Regards,
Tom Dagostino
971-279-5325
tom@xxxxxxxxxxxxxxxxx<mailto:tom@xxxxxxxxxxxxxxxxx>
[LogoAddress]
From: ibis-macro-bounce@xxxxxxxxxxxxx<mailto:ibis-macro-bounce@xxxxxxxxxxxxx>
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Muranyi, Arpad
Sent: Thursday, July 20, 2017 2:54 PM
To: IBIS-ATM; IBIS-Interconnect
Subject: [ibis-macro] BIRD189 and NC pins
Hello Everyone,
One of my colleagues asked me another interesting question. This is about the
NC pins.
I searched BIRD189 for "NC" and "no-connect". NC appears only in the [Pin] and
[Pin
Mapping] keywords of the examples, and in one sentence where both NC and
no-connect
appears once, explaining the pint types in the [Pin] keyword.
The IBIS spec does not give much more detail on defining what an NC pin really
is.
The question is this: Does NC mean that we are not making any connections to
that pin
on the inside of the component (i.e. the package side of the pin), or are we
saying that
nothing should be connected to the pin from the board side?
The reason this question was raised is because we were wondering whether BIRD189
allows or prohibits any interconnect/package models to involve NC pins. The
BIRD
doesn't say anything on that. Does it mean that one could make a package model
which goes to an NC pin? After all, I have seen chips in which NC meant that
the user
should not connect anything to the NC pin on the board, while the chip did have
stuff
connected to it from the inside (probably for super-secret testing purposes,
etc...).
Thanks,
Arpad
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