81，Verilog-2005标准篇：port端口介绍

端口为由模块和基元组成的硬件描述提供了一种互连方式。端口/端口列表的标准语法如下表1所示：

表1：端口/端口列表语法定义

端口声明的语法如下表2所示：

表2：端口声明的语法定义

例子1：

有符号（signed）属性可以附加在端口port声明或相应的net或reg声明上，也可以同时附加在这两个声明上。如果端口或net/reg 被声明为signed，则另一个也应被视为signed。

隐式net应视为无符号net信号，连接到端口的net信号如果没有明确的有符号声明，则应视为无符号net信号，除非该端口被声明为有符号net。

例子2：

module  test(a,b,c,d,e,f,g,h);
input  [7:0] a;   // no explicit declaration - net is unsigned
input  [7:0] b;
input   signed  [7:0] c;
input   signed  [7:0] d;  // no explicit net declaration - net is signed
output  [7:0] e;   // no explicit declaration - net is unsigned
output  [7:0] f;
output   signed  [7:0] g;
output   signed  [7:0] h;  // no explicit net declaration - net is signed
wire signed  [7:0] b; // port b inherits signed attribute from net decl.
wire [7:0] c;  // net c inherits signed attribute from port
reg  signed  [7:0] f; // port f inherits signed attribute from reg decl.
reg  [7:0] g;  // reg  g inherits signed attribute from port
endmodule

module  complex_ports ({c,d}, .e(f)); 
// Nets {c,d} receive the first port bits.
// Name 'f' is declared inside the module.
// Name 'e' is defined outside the module.
// Can't use named port connections of first port.
module  split_ports (a[7:4], a[3:0]);
// First port is upper 4 bits of 'a'.
// Second port is lower 4 bits of 'a'.
// Can't use named port connections because of part-select port 'a'.

module  same_port (.a(i), .b(i));
// Name 'i' is declared inside the module as an inout port.
// Names 'a' and 'b' are defined for port connections.

module  renamed_concat (.a({b,c}), f, .g(h[1])); 
 // Names 'b', 'c', 'f', 'h' are defined inside the module.
 // Names 'a', 'f', 'g' are defined for port connections.
 // Can use named port connections.

module  same_input (a,a);
input  a; // This is legal. The inputs are tied together.
module  mixed_direction (.p({a, e}));
input  a; // p contains both input and output directions.
output  e;

上面的例子中，端口的定义太冗杂，verilog标准提供了另一种非常简单的端口定义和声明方法，每个声明的port端口都提供了有关端口的完整信息。端口的方向、位宽、net或variable类型，以及端口是有符号sigend还是无符号unsigned，都有完整的描述。例子如下：

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