Verilog 常用操作符，以及$display系统函数 ModelSim 仿真

verilog的操作符主要包括—
算数操作符、Arithmetic Operators
关系操作符、Relational Operators
相等操作符、Equality Operators
逻辑操作符、Logical Operators
按位操作符、Bit-wise Operators
归约操作符、Reduction Operators （也叫缩减运算符）
移位操作符、Shift Operators
条件操作符、Conditional Operators
连接操作符、Concatenation Operator
赋值操作符、assignment operator;

一、算术操作符、Arithmetic Operators

Operator	Description
+	binary plus
-	binary minus
*	multiply
/	divide
+	unary (sign) plus 符号操作符
-	unary (sign) minus 符号操作符

仿真代码

module arithmetic_operators();

initial begin
  $display (" 5  +  10 = %d", 5  + 10);
  $display (" 5  -  10 = %d", 5  - 10);
  $display (" 10 -  5  = %d", 10 - 5);
  $display (" 10 *  5  = %d", 10 * 5);
  $display (" 10 /  5  = %d", 10 / 5);
  $display (" 10 /  -5 = %d", 10 / -5);
  $display (" 10 %s  3  = %d","%", 10 % 3);
  $display (" +5       = %d", +5);
  $display (" -5       = %d", -5);
  #10 $finish;
end

endmodule

仿真：
1.打开modlesim， File – new – source ,输入上面的代码。

2. Saveas

3. 点击compile，找到刚才存储文件的路径，选中文件。会提示是否创建work文件夹，先点击Compile，然后点击done。
   

4. 点击simulate，在弹出串口中，点击最上面work前面的加号，选中跟module相同名字的选项，点右下角OK。

5. 在下面的transcript串口输入run命令，会弹出窗口问你是否结束，这里一定要选NO！选yes会退出程序。
   看到$display 运行的结果。
   

二、关系操作符、Relational Operators

关系操作符的结果为1或0，即真或假。

Operator	Description
a < b	a less than b
a > b	a greater than b
a <= b	a less than or equal to b
a >= b	a greater than or equal to b

仿真代码

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module relational_operators();

initial begin
  $display (" 5     <=  10 = %b", (5     <= 10));
  $display (" 5     >=  10 = %b", (5     >= 10));
  $display (" 1'bx  <=  10 = %b", (1'bx  <= 10));
  $display (" 1'bz  <=  10 = %b", (1'bz  <= 10));  
  #10 $finish;
end

endmodule

仿真步骤可以参照上面的算术操作符里提到的，这里省略了，只贴出结果。

	
  5     <=  10 = 1
  5     >=  10 = 0
  1'bx  <=  10 = x
  1'bz  <=  10 = x

三、相等操作符、Equality Operators

Operator	Description
a === b	a equal to b, including x and z (Case equality)
a !== b	a not equal to b, including x and z (Case inequality)
a == b	a equal to b, result may be unknown (logical equality)
a != b	a not equal to b, result may be unknown (logical equality)

仿真代码：

module equality_operators();

initial begin
  // Case Equality
  $display (" 4'bx001 ===  4'bx001 = %b", (4'bx001 ===  4'bx001));
  $display (" 4'bx0x1 ===  4'bx001 = %b", (4'bx0x1 ===  4'bx001));
  $display (" 4'bz0x1 ===  4'bz0x1 = %b", (4'bz0x1 ===  4'bz0x1));
  $display (" 4'bz0x1 ===  4'bz001 = %b", (4'bz0x1 ===  4'bz001));
  // Case Inequality
  $display (" 4'bx0x1 !==  4'bx001 = %b", (4'bx0x1 !==  4'bx001));
  $display (" 4'bz0x1 !==  4'bz001 = %b", (4'bz0x1 !==  4'bz001));  
  // Logical Equality
  $display (" 5       ==   10      = %b", (5       ==   10));
  $display (" 5       ==   5       = %b", (5       ==   5));
  // Logical Inequality
  $display (" 5       !=   5       = %b", (5       !=   5));
  $display (" 5       !=   6       = %b", (5       !=   6));
  #10 $finish;
end

endmodule

仿真结果：

四、逻辑操作符、Logical Operators

Operator	Description
!	logic negation 逻辑取反
&&	logical and
||	logical or

仿真代码：

module logical_operators();

initial begin
  // Logical AND
  $display ("1'b1 && 1'b1 = %b", (1'b1 && 1'b1));
  $display ("1'b1 && 1'b0 = %b", (1'b1 && 1'b0));
  $display ("1'b1 && 1'bx = %b", (1'b1 && 1'bx));
  // Logical OR
  $display ("1'b1 || 1'b0 = %b", (1'b1 || 1'b0));
  $display ("1'b0 || 1'b0 = %b", (1'b0 || 1'b0));
  $display ("1'b0 || 1'bx = %b", (1'b0 || 1'bx));
  // Logical Negation
  $display ("! 1'b1       = %b", (!  1'b1));
  $display ("! 1'b0       = %b", (!  1'b0));
  #10 $finish;
end

endmodule

仿真结果：

五、按位操作符、Bit-wise Operators

Operator	Description
~	negation
&	and
|	inclusive or 同或
^	exclusive or 异或
^~ 或 ~^	exclusive nor (equivalence)

按位操作有时会不容易观察，特别是多个运算符在一起的时候，为了避免阅读上的障碍，尽量多用括号。

仿真代码

module bitwise_operators();

initial begin
  // Bit Wise Negation
  $display (" ~4'b0001           = %b", (~4'b0001));
  $display (" ~4'bx001           = %b", (~4'bx001));
  $display (" ~4'bz001           = %b", (~4'bz001));
  // Bit Wise AND
  $display (" 4'b0001 &  4'b1001 = %b", (4'b0001 &  4'b1001));
  $display (" 4'b1001 &  4'bx001 = %b", (4'b1001 &  4'bx001));
  $display (" 4'b1001 &  4'bz001 = %b", (4'b1001 &  4'bz001));
  // Bit Wise OR
  $display (" 4'b0001 |  4'b1001 = %b", (4'b0001 |  4'b1001));
  $display (" 4'b0001 |  4'bx001 = %b", (4'b0001 |  4'bx001));
  $display (" 4'b0001 |  4'bz001 = %b", (4'b0001 |  4'bz001));
  // Bit Wise XOR
  $display (" 4'b0001 ^  4'b1001 = %b", (4'b0001 ^  4'b1001));
  $display (" 4'b0001 ^  4'bx001 = %b", (4'b0001 ^  4'bx001));
  $display (" 4'b0001 ^  4'bz001 = %b", (4'b0001 ^  4'bz001));
  // Bit Wise XNOR
  $display (" 4'b0001 ~^ 4'b1001 = %b", (4'b0001 ~^ 4'b1001));
  $display (" 4'b0001 ~^ 4'bx001 = %b", (4'b0001 ~^ 4'bx001));
  $display (" 4'b0001 ~^ 4'bz001 = %b", (4'b0001 ~^ 4'bz001));
  #10 $finish;
end

endmodule

仿真结果

六、归约操作符、Reduction Operators
也叫缩减运算符、递减运算符，这部分请参照之前的一篇博文
https://blog.csdn.net/malcolm_110/article/details/90487935

七、移位操作符、Shift Operators

Operator	Description
<<	left shift
>>	right shift

仿真代码

module shift_operators();

initial begin
  // Left Shift
  $display (" 4'b1001 << 1 = %b", (4'b1001 << 1));
  $display (" 4'b10x1 << 1 = %b", (4'b10x1 << 1));
  $display (" 4'b10z1 << 1 = %b", (4'b10z1 << 1));
  // Right Shift
  $display (" 4'b1001 >> 1 = %b", (4'b1001 >> 1));
  $display (" 4'b10x1 >> 1 = %b", (4'b10x1 >> 1));
  $display (" 4'b10z1 >> 1 = %b", (4'b10z1 >> 1));
  #10 $finish;
end

endmodule

仿真结果

	
  4'b1001 << 1 = 0010
  4'b10x1 << 1 = 0x10
  4'b10z1 << 1 = 0z10
  4'b1001 >> 1 = 0100
  4'b10x1 >> 1 = 010x
  4'b10z1 >> 1 = 010z

八、条件操作符、Conditional Operators

条件操作符就是代码中常见的形式如下的结构
cond_expr ? true_expr : false_expr

九、连接操作符、Concatenation Operator

连接操作符的作用就是实现位拼接。

{
    
    a[3:0], 4'b1001}

结果为8位。
还有一种叫Replication Operator，重复连接操作，形如：
{3{a}}
效果等同于 {a, a, a}

十、赋值操作符、assignment operator

Operator	Description
=	blocking assignment
<=	Non-blocking assignment

blocking assignment 阻塞赋值，用于组合逻辑里面，赋值不分先后顺序，可能造成竞争与冒险。
Non-blocking assignment 非阻塞赋值，用于时序逻辑里面，赋值是分先后顺序，这部分可参考其它资料。