三态门主要有bufif0/bufif1/notif0/notif1
三态门使能们用实例声明语法：
选通实例化：3360=* * enable _ gate _ instance ([ delay3] * * enable _ gate )；
*使能门类型* * :3360=buf if0|buf if1|notif0| notif 1
**enablementage实例* * :=[ name _ of _ instance ] (output _ terminal，input_terminal，enable_terminal )
1.驱动强度规格
anoptionaldrivestrengthspecificationshallspecifythestrengthofthelogicvaluesontheoutterminalsofthegateinstance。
thedrivestrengthspecificationforagateinstance，witheexceptionofpullupandpulldown，shallhaveastrength1specificationanandastion
* the strength1specificationshallspecifythestrengthofsignalswithalogicvalue 1，and the strength0specificationshalllspecifythestreng
the strength1specificationshallbeoneofthefollowingkeywords 3360
supply1 strong1 pull1 weak1
the strength0specificationshallbeoneofthefollowingkeywords 3360
supply0 strong0 pull0 weak0
specifyinghighz1as strength1shallcausethegateorswitchtooutputalogicvaluezinplaceofa 1。
specifyinghighz0shallcausethegatetooutputalogicvaluezinplaceofa 0。
thestrengthspecifications (highz 0，highz1) and ) highz1，highz0) shall be considered invalid。
* intheabsenceofastrengthspecification，theinstancesshallhavethedefaultstrengthsstrong1and strong0. * *
2.延迟规格
anoptionaldelayspecificationshallspecifythepropagationdelaythroughthegatesandswitchesina
解释。
* gatesandswitchesindeclarationswithnodelayspecificationshallhavenopropagationdelay.* *
adelayspecificationcancontainuptothreedelayvalues，depending on the gate type。
thepullupandpulldowninstancedeclarationsshallnotincludedelayspecifications。
3.三态门真值表如下
thefollowingexampledeclaresaninstanceofbufif 1:
*bufif1BF1(outw，inw，controlw )； **
The output is outw，the input is inw，andthecontroliscontrolw.theinstancenameisbf 1。
thedelayspecificationshallbezero，one，two，or three delays。
1.ifthedelayspecificationcontainsthreedelays，thefirstdelayshalldeterminetherisedelay， theseconddelayshalldeterminethefall thethirddelayshalldeterminethedelayoftransitionstoz，andthesmallestofthethreedelayssshallded
2.ifthespecificationcontainstwodelays，thefirstdelayshalldeterminetheoutputrisedelay，theseconddelayshalldeterminetheoutputpup
3.If only one delay is specified，itshallspecifythedelayforalloutputtransitions。
4.ifthereisnodelayspecification，thereshallbenopropagationdelaythroughthegate。