Frm: IEEE Std 1364?-2001, IEEE Standard Verilog? Hardware Description Language
The tri0 and tri1 nets model nets with resistive pulldown and resistive pullup devices on them. When no driver drives a tri0 net, its value is 0. When no driver drives a tri1 net, its value is 1. The strength of this value is pull. See Clause 7 for a description of strength modeling.
A tri0 net is equivalent to a wire net with a continuous 0 value of pull strength driving it. A tri1 net is equivalent to a wire net with a continuous 1 value of pull strength driving it.
A truth table for tri0 is shown in Table 6. A truth table for tri1 is shown in Table 7.
原文：http://www.cnblogs.com/qiyuexin/p/6385846.html