雙向通過開關主要有tran/rtran/tranif0/tranif1/rtranif0/rtranif1
當tranif0,tranif1, rtranif0, or rtranif1設備關閉時，它們應該阻塞信號。當打開時，它們應該通過信號。而tran and rtran 設備不能被關閉，它們一直通過信號。
實例tranif1聲明語法：
tranif1 t1 (inout1,inout2,control);
1.延遲規格
The delay specifications for** tranif1, tranif0, rtranif1, and rtranif0 **devices shall be zero, one, or two delays.
If the specification contains two delays, the first delay shall determine the turn-on delay, the second delay shall determine the turn-off delay, and the smaller of the two delays shall apply to output transitions to x and z.
If only one delay is specified, it shall specify both the turn-on and the turn-off delays.
If there is no delay specification, there shall be no turn-on or turn-off delay for the bidirectional pass switch.
雙向通過開關tran和rtran沒有延遲使用。
The tranif1, tranif0, rtranif1, and rtranif0 devices shall have three items in their terminal lists.
前兩個選項是信號輸入與輸出信號，第三個是輸出信號控制開關。
這兩個開關tran和rtran包含兩個雙向信號。這六個開關應該是標量網線或向量位選。
這些開關tran, tranif0, and tranif1 只有一種情況會改變通過信號的強度, as discussed in 28.15.1. 這些開關rtran, rtranif0, and rtranif1 會降低通過它們信號的強度,as discussed in 28.14.