You're right, at least in Verilog-XL !

That's an even worse bug! Now I consider fixing this in the LRM
as critical!

Let me explain.

In any standard, it is accepted that where there is a conflict between
the verbal

description and the formal description, then the formal description
takes precedence.

In this case, the formal description is the truth tables in Tables 3-5
and 3-6,

which make no reference to strength. For example, 3-5 shows that if
a tri0 is

driven with a 1, regardless of strength, then the wire is never 0.

Note that the corresponding truth tables 3-2 to 3-4 have the comment,

"Note that they assume equal strengths for both drivers".

Furthermore, I raised this issue way back in October 2000,

and nobody contradicted me then.

If I could interpret this wrongly, than others are liable to do
so as well.

Therefore, the correct fix is:

- Delete the sentences:

"When no driver drives a tri0 net, its value is 0. When no driver drives
a tri1 net, its value is 1.

The strength of this value is pull."

- Delete the sentences:

"A truth table for tri0 is shown in Table 3-5. A truth table
for tri1 is shown in Table 3-6."

- Delete Table 3-5 and 3-6.

Thanks, Steven.

Shalom

 

 

Steven Sharp wrote:
<blockquote TYPE=CITE>Sorry Shalom, but you have this backwards.

>The descriptions of tri0 and tri1 in section 3.7.4 are inaccurate and

misleading.

Slightly misleading anyway.

>The accurate sentence (for tri1) is "When no driver drives a tri1 net,
its

value is 1."

No, that is the one that is misleading.  It happens to be true,
but does

not specify its full effect.

>Inaccurate are

>"The tri0 and tri1 nets model nets with resistive pulldown and resistive
pullup

devices on them," and "A tri1 net is

>equivalent to a wire net with a continuous 1 value of pull strength
driving

it."

This is the one that is accurate and complete.

>The difference occurs if the net is being driven by a driver weaker
than pull.

>In a true pullup net, the pullup will override the driver. In a tri1,
the weak

driver will succeed.

>Similarly, if a true pullup net is also driven by a pull0

>strength, there will be contention, but not in a tri1 net.

Yes, that is when the difference occurs.  If you try this in Verilog-XL,

you will find that a tri1 acts exactly like a net with an implicit
pullup.

>Note that the second inaccurate sentence does not appear in 1364-1995.

The second sentence was added to clarify the misleading one from 1364-1995.

>At the very least, the second inaccurate sentence, which was

>added in 1364-2001 should be deleted.

The first sentence is an oversimplification and obviously could be

misleading.  Perhaps it should be modified.  However, the
second

sentence acts to clarify the meaning of the first sentence.

Steven Sharp

sharp@cadence.com

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