Talk:Don't-care

Merge
The other I have reached over disambigouition from Don't Care (note the capital letter). I think simply redirecting the other to this page would do it. But this is a job for a more experienced person, greetings from de.WP --Biezl (talk) 17:24, 18 July 2008 (UTC)

Sure?
In VHDL, don't cares are expressed by "-" and can be used for optimization. "X" and "W" are strong/weak unknowns, they are not used for optimization. They occur when two different weak or two strong signals collide, like "0" and "1" on the same signal. "U" means that a signal has not been initialized yet, like the flip flop mentioned. "X", "W" and "U" are only set by the simulation software, and do not occur in real circuits (as mentioned in the article), and it makes no sense to set them in the VHDL code. On the other hand, "-" is set by the designer, simulation will never generate a don't care (except when a signal is "driven" by "-"). I think the article shoud mention that "W", "X" and "U" are NOT don't cares which are used for optimization; they are undefined values to show non-realistic behaviour. —Preceding unsigned comment added by 85.180.25.51 (talk) 20:33, 6 August 2008 (UTC)