Subject: BIRD 7 (more from Kellee Crisafulli)

From: Kellee Crisafulli <[email-masked]>
Date: 21 Jan 94 03:09:34 EST

From: Kellee Crisafulli, HyperLynx

To: Bob Ross, Bob Ward and fellow IBISers

Re: BIRD 7, Resending, (1/2 of the document was lost in the mail)

For some reason only 1/2 of my Email was transmitted.  I recreated the
the 2nd 1/2 from memory and am resending it.

Also, at the end of this document is my response to Bob's last message.

My apologies, I don't know where the other 1/2 landed ...
(perhaps in the IBIS bird bath)

Bob, I basically like what you have proposed in BIRD 7 for the additional
key words. I have been going to send in a bird on this, but have been
waiting for the results of an in-house project we are doing to develop some 
ABT models under IBIS.   We have nearly completed this project and I can 
report on this now.    

I also have a few concerns with bird 7, specifically:
  1) I believe we absolutely must address the dv/dt issue for the turn off
     side.  We could do this by simplystating explicitly in the 
     specification that the dv/dt associated with opposite side is used as 
     the turn-off time of the open-side device.   However it must include a 
     load specification during turn off. and specify this being valid for
     the a load resistor to the opposite rail.

  2) I think it would be very useful to most semi-conductor companies 
     developing models to require that V/I table data match the model type 
     exactly.  This way the IBIS parse can check it and help find errors in 
     manually entered data.

  3) If I am not mistaken CMOS has an open_drain p channel and an open_drain
     N channel device there is no open_source configuration that I know of
     unless you consider some of the 3 volt outputs with totem  pole type 
     N-channel outputs.  Therefore the key word open_source may not be 
     appropriate.  I propose instead that we use just Open_drain to indicate 
     either an N channel/P channel, open collector, or open emitter type 
     output.  The thing that differentiates them is simply the missing V/I 
     data for the output.

HyperLynx now has IBIS simulations running of ABT buffers (FutureBus) which 
look pretty good.  These require the open_drain model type and have an 
additional offset for the output diode.  I therefore feel good about 
recommending the use of IBIS for modeling open side devices.

I beleive we should modify BIRD7 as follows:
*********************************************

1) Modify the "Usage Rules" under the Keyword Model, to show Open_drain
   instead of Open-drain. (exactly as Bob suggested)

2) Add only one new keyword "I/O_open_drain" to the list in usage rules, 
   and the Model_type line.  This keyword allong with Open_drain can 
   represent all open side devices.  The absence of either the Pullup and 
   Pulldown V/I table can be used to indicate which side is open.

3) Change the section titled NOTES ON DATA DERIVATION METHOD as follows:

  Section 3 on Ramp rates:
  ------------------------
  3) Ramp Rates:
     The ramp rates (listed in AC characteristics below) should be derived 		
     as follows:
       1)Start with the silicon model, remove all packaging.

       2)If: The model type is one of the following: Output, I/O, or 3-state 
         Then: Attach a 50 ohm resistor to GND to derive the rising edge 
               ramp.
	       Attach a 50 ohm resistor to POWER to derive the falling
               edge ramp.

	 If: The model type is either (Open_drain or I/O_open_drain) and 
             the Pullup V/I table is missing.
         Then: Attach either a 50 ohm resistor or the vendor suggested 
               termination resistance to either POWER or the vendor suggested
               termination voltage.  Use this load to derive both the rising
               and falling edges.

         If: The model type is either (Open_drain or I/O_open_drain) and
             the Pulldown V/I table is missing.
         Then: Attach either a 50 ohm resistor or the vendor suggested
               termination resistance to either GND or the vendor suggested
               termination voltage.  Use this load to derive both the rising
               and falling edges.

	4-6) renumber these 3-5

	7) **** Delete item 7 ******

4) Under the Pullup, Pulldown keyword section in usage rules, add the
   following:

        If the model type is (Output, I/O, or 3-state) then both the Pullup
        and Pulldown V/I tables are required.

        If the model type is either (Open_drain or I/O_open_drain) then
        only one "Pull" V/I table (Pullup or Pulldown) may be present.

Postmortum:
-----------
After reading Bobs response to 1/2 of my Email I agree that the usage
of open_source is being used by some vendors in a somewhat confusing manor.
i.e. they call the open drain P channel devices open_source.  While I think
this is an inconsistant usage, I am willing to use Open_source and
I/O_open_source as Bob suggested if the entire IBIS group strongly perfers
this.

I DO NOT however want to choose a solution that deletes the existing
Open_drain model type as this is not backward compatible with the
specification.

Note: 3_state_open_drain is a redundant definition and is therefore not
needed. (i.e. open_drain by definition is 3-stated if it is off)

Summary:
--------
Using just two key words, Open_drain, and I/O_open_drain is simple, and
maintains backward compatibility, and covers all the cases so far...

P.S. thankyou for the Fax, Bob.

Best wishes to all...... Kellee