2023.12.15

QnA

assign关键词的含义

  • continuous assignment (net) uses ⭐assign [Syntax 6-1]
  • procedural assignment (variable) [Syntax 6-2]
  • procedural continuous assignment (net or variable) [Syntax 9-3]
    • variable uses ⭐assign/deassign
    • net uses force/release

[TODO] always关键词的含义？

4. Data types

4.1 Value set

high-impedance 高阻态

value set:

  • 0
  • 1
  • x (unknown)
  • z (high-impedance)

本科的时候不理解z，主要是是以为电路真的就是0电压和高电压。 但是0和1其实应该是对应正负电压。 现在再去看看wikipedia的定义，很多概念真的很简单了。

有关高阻态很有意思的一句话

When the z value is present at the input of a gate or when it is encountered in an expression, the effect is usually the same as an x value. Notable exceptions are the metal-oxide semiconductor (MOS) primitives, which can pass the z value

TODO: 所以MOS半导体技术包含哪些？ 看来Verilog可以包含多种半导体技术的电路，怎么声明用某种半导体技术？

11 Scheduling semantics

The elements that make up the Verilog HDL can be used to describe the behavior, at varying levels of abstraction(2008.Verilog数字系统设计教程.夏宇闻.ocr.md: 第二章列了5个层次), of electronic hardware. An HDL has to be a parallel programming language.

Although the Verilog HDL is used for more than simulation, the semantics of the language are defined for simulation, and everything else is abstracted from this base definition.

11.6.1

A continuous assignment ... sensitive to the source elements in the expression.