BIRD 70.3 open issues

As we discussed in the Open Forum call this morning, there are two
unresolved issues related to BIRD 70.3. I would like to clarify the issues
in this note and propose a resolution to them so we can move on to a vote.

Issue 1: Different inverting and non-inverting drivers

This is a legal scenario within IBIS and should be covered by BIRD 70.3. I
propose we add a new subparameter Driver_model_inv under [Test Data]. This
subparameter is only legal when Test_data_type is differential.

I think this is a pretty straight-forward solution to the issue. Any
discussion?

Issue 2: Legal combinations of Test_data_type and Test_load_type

Here are the possible combinations:

Case 1: Test_data_type = Single_ended, Test_load_type = Single_ended
Case 2: Test_data_type = Single_ended, Test_load_type = Differential
Case 3: Test_data_type = Differential, Test_load_type = Single_ended
Case 4: Test_data_type = Differential, Test_load_type = Differential

Cases 1, 2 and 4 are clear. Cases 1 and 4 are clearly allowed, and Case 2
is clearly NOT allowed. In my opinion, Case 3 should be illegal. If one
wanted to capture singled-ended waveforms for a differential driver, one
could use Case 1 and just specify the differential driver. I don't see any
differences between Case 1 and Case 3. Are there any?

Incidentally, this also implies that [Rising Waveform] (and its companions)
is legal only for Test_data_type = Single_ended and [Diff Rising Waveform]
is legal only for Test_data_type = Differential. I like this solution.
It's simple, and it covers the space defined by IBIS.

Al Davis proposed a new keyword, [Common Mode Rising Waveform Near], but my
gut reaction to this is negative. First, I want to close the BIRD since
it's been on the table a long time and is holding up IBIS 4.0. Second, it
seems somewhat verbose.

I propose that Cases 1 and 4 be legal but Cases 2 and 3 be illegal. Any
objections?

Greg Edlund
Electrical Packaging
IBM Server Technology Development
3605 Hwy. 52 N, Dept. HDC
Rochester, MN 55901
gedlund@us.ibm.com

On Fri, 04 May 2001, Gregory R Edlund wrote:
> BIRD 70.3 has four new keywords for differential waveforms.
>
> I removed the "timing-related" subparameters in favor of using an
> extra set of Golden Waveforms that
> specify the standard (timing) test load.
>
> There is still one outstanding issue: what are the legal
> combinations of test_data_type and test_load_type?

That's easy. Just say they need to be the same.

It needs clarification of the meaning of the various waveforms, and
which can be used with which type.

Something like:

Diff waveforms are only used with type differential, and are measured
differentially. The other waveforms may be used with either
single_ended or differential types. When used with the differential
type, they represent the common mode waveforms, measured from one
side to ground.

It would probably be an improvement to explicitly say they are
common-mode, as in [Common Mode Rising Waveform Near], so the Diff or
Common forms are used with type differential, and the plain is used
with single-ended. Reason: the plain one will be interpreted as the
most significant, but in differential mode the differential one
really is.

 
Received on Fri Jun 1 10:07:37 2001