Where X=verilog

First I would like to thank Hackman since a lot of the verilog stuff I learned comes from his website! His verilog article. There is a lot more to verilog that I still have to learn but these are the basics, I will continually come back and upgrade the page when I feel the need to.

Btw if you don’t know this is written in the style of learnxinyminutes.com, I just decided to make mine because they don’t have one for verilog.

Simple hello world example:

initial $display("Hello, world!");

Declaring a module looks like this:

module top_module (
    input a,
    output b
    );
endmodule

## Instantiation of a module looks like this:

module tb;
    wire a;
    reg b;

    top_module dut(
        .a(a),
        .b(b)
        );
endmodule

Assigning signals looks like this:

assign b = a;

Simple diagram of the module `top_module`:

// a->□->b

Wires and Registers:

// Wires are just there to connect different elements, they are driven by continuous assign statements or module ports. 
//They can be thought of as physical wires.

Buses or Vectors:

// Buses or Vectors let you extend your ports or signals by giving them a range of n-bits.
// They're usually written from MSB to LSB although it doesn't really matter.
// Ex with an 8-bit input port:
input [7:0] hehe;

// Assign n-wire to an output:
assign out = hehe[4];

Number Representations:

// Numbers in verilog can represented in multiple number systems like hex, octal, decimal or binary.
// The syntax is as follows:
// w'snnn
// w = width of digit(s) (how many bits it uses) 
// s = number system
// nnn = the actual numbers
// Binary example:
8'b01010101;

// Hex example:
2'h55;

// Decimal example:
2'd85;

// Octal example:
3'o125;
// Notice I've used the exact same value for each example.

Operators:

// NOT = ~
// AND = &
// OR = |
// XOR = ^
// NOR = ~( x | y )
// NAND = ~( x & y )
// Logical Operators are the same as for any other programming language.

IF statement:

if (condition) begin
  // code to execute if true;
end else begin
  // code to execute if not true;
end

Delays:

// Delays tell the program how many time units to wait before executing a line of code. Similar to the sleep command in shell.
#20; // code goes here;

Always blocks:

// Always, is a procedural block. It can be used as a set of instruction or as a statement.
// Statement example:
always #5 clk = ~clk;

// Block example that tells the program to execute the code block whenever the stop signal is true:
always @(stop) begin
    // code goes here;
end

// More common block example that executes on the positive edge of a clock signal/cycle:
always @(posedge clk) begin
    // code goes here;
end
// I think of the always blocks as being if statements inside a while true.