bufif1

[GaLaKtIkUs™]

Hi everybody
Is there any difference between:
bufif1(out,in,ctrl);
and:
assign out=ctrl?in:1'bz

Cheers
Mehdi

 

[Cary R.]

GaLaKtIkUs™ wrote:

Hi everybody
Is there any difference between:
bufif1(out,in,ctrl);
and:
assign out=ctrl?in:1'bz

Yes, look at how the two respond when the control signal is undefined or
high-Z and the input has a defined value. This difference is observable
if you have some kind of pull on the output. One always returns 1'bx
while the other will return a defined value if the input and the pull
are in the same direction.

Cary

 

[Dave Rich]

On Mar 29, 11:34 am, "Cary R." <no-s...@host.spam> wrote:

GaLaKtIkUs™ wrote:
Hi everybody
Is there any difference between:
bufif1(out,in,ctrl);
and:
assign out=ctrl?in:1'bz

Yes, look at how the two respond when the control signal is undefined or
high-Z and the input has a defined value. This difference is observable
if you have some kind of pull on the output. One always returns 1'bx
while the other will return a defined value if the input and the pull
are in the same direction.

Cary

The difference is that a gate-level primitive can drive a range of
strengths, whereas a continuous assignment statement can only drive a
single strength. Strengths can have a range starting from Supply0
through High-Z and up to Supply1. A unknown is typically represented
as a range of strengths from Strong0 to Strong1. When the control
signal to the bufif1 is unknown, the output will drive a range of
strengths from High-Z to Strong0 or High-Z to Strong1, depending on
the state of the input.

When resolving the state of wires with multiple drivers, if all
strengths are one side of high-Z, 0 or 1, that is used at the state of
the wire for logic expressions. If there are strengths on either side,
the strongest strength wins. Then if you have two drivers on a wire,
one driven by a bufif1 with a strength range of High-Z to Strong1, and
another driving Pull1, thew wire will resolve as have a strength range
of Strong1 to Pull1, which is a logic 1.

Dave