Subject: RE:analog pins in IBIS - request for clarification

From: Roland Chang <[email-masked]>
Date: Mon, 23 Jun 1997 14:08:51 -0700

As I understand it, I should put "NC" as the model name in the [Pin]
section for analog pins, but I have a few follow-up questions as well
that I hope people can answer for me.

What is the difference between including the analog pin under the [Pin]
keyword, and then putting "NC" beside it, 
versus omitting the pin altogether?  

Also, if I specify an analog pin in the [Pin] section with "NC" what
should I put in the [Pin Mapping] section for that pin?  (Incidentally,
I know which power buses power up the analog pins) For example, say I
knew that pins 5 and 9 are analog power and ground for pin 10( which is
an analog pin), would it hurt to list pins 5 and 9 as the pullup and
pulldown reference for pin 10?

What if the analog pins that I am dealing with are a set of differential
pins (+) and (-) pair, do I include them in the [Diff Pin] section as
well? even though they have no  vdiff specification? and have "NC" as
their model in the [Pin] section?

Finally, this may be a really stupid question, but I feel that I don't
quite understand why IBIS doesn't handle analog pins. Could someone
please enlighten me on this matter?  

Again, your help is much appreciated,

Roland Chang

******************************************
Roland Chang ext. 2647

PMC-Sierra 
Applications Department
105-8555 Baxter Place
Burnaby, BC
V5A 4V7
Tel: (604) 415-6000

email: [email-masked]
******************************************
>-----Original Message-----
>From:	Andy Ingraham [SMTP:[email-masked]]
>Sent:	June 15, 1997 2:44 PM
>To:	Roland Chang; Roland Chang; [email-masked]
>Cc:	[email-masked]; [email-masked]
>Subject:	RE: IBIS component generation, PECL differential inputs, analog I/O
>pins, Vmeas, Cref, Rref, Vref 
>
>> >  Thirdly, how are analog I/O pins treated in IBIS and s2ibis2?  How would
>> >  I setup an analog I/O pin in s2ibis2 and IBIS?
>> 
>> 	Scope of IBIS is restricted to analog behaviour of Digital ICS. 
>> 	I am not sure what you really mean by analog I/O pin ?. 	
>
>On a mixed-signal IC, analog pins would not have models in the IBIS
>file.
>
>It seems like one might use "NA" as the model_name under the [Pin]
>keyword, to signify that these pins have no available IBIS data. 
>However, that is not allowed.  Instead, use "NC".  Technically
>incorrect, but it tells the IBIS parser to skip those pins.
>
>[Pin]   signal_name     model_name      R_pin   L_pin   C_pin
>|
>  1     RAS0#           Buffer1         200.0m  5.0nH   2.0pF
>  2     RAS1#           Buffer2         209.0m  NA      2.5pF
>  3     Analog_out      NC
>...
>
>Regards,
>Andy Ingraham