How can a net have multiple strengths?

[kevin arnold]

Hi All,
LRM Section 7.10.2 refers to nets with mutliple levels of strength.
This is not quite clear. How can a net have multiple levels of strength
associated with it? At any point of time the value can 0/1/z/x.

Regards

 

kevin arnold wrote:

LRM Section 7.10.2 refers to nets with mutliple levels of strength.

This is not quite clear. How can a net have multiple levels of
strength
associated with it? At any point of time the value can 0/1/z/x.

Well, to start with, a net with a value of X can clearly have more than
one level of strength associated with it: the strength of the possible
0
and the strength of the possible 1. This can be obtained just by
having
a driver which has a different 0 and 1 strength, and which is driving
X.
The tristate buffer primitives (e.g. bufif0) introduce more
possibilities.
For example, if the data input is 0 and the control input is X, then
the
output is either 0 or Z. This is sometimes called L, but is simply an
output value of X with the 0 strength of the driver (typically
strong0),
but a 1 strength of HiZ.

Combining drivers of these different strength/value combinations
driving
the same net can result in other combinations, including ones which
have
a definite value of 0 or 1 but with a possible strength range. The LRM
section you referenced contains many examples and explanations of these
situations.