经典IC设计面试问题9

yanzhang98 · 发表于 2010-11-28 04:26:06

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x

Casex,z difference,which is preferable,why?

CASEZ :
Special version of the case statement which uses a Z logic value to represent don't-care bits. CASEX :
Special version of the case statement which uses Z or X logic values to represent don't-care bits.

CASEZ should be used for case statements with wildcard don抰 cares, otherwise use of CASE is required; CASEX should never be used.
This is because:
Don抰 cares are not allowed in the "case" statement. Therefore casex or casez are required. Casex will automatically match any x or z with anything in the case statement. Casez will only match z抯 -- x抯 require an absolute match.