2. Lexical Tokens

Verilog source text files consists of the following lexical tokens:

• White Space

White spaces separate words and can contain spaces, tabs, new-lines and form feeds. Thus a statement can extend over multiple lines without special continuation characters.

• Comments

Comments can be specified in two ways ( exactly the same way as in C/C++ ):

• Begin the comment with double slashes (//). All text between these characters and the end of the line will be ignored by the Verilog compiler.

• Enclose comments between the characters /* and */. Using this method allows you to continue comments on more than one line. This is good for “commenting out” many lines code, or for very brief in-line comments.

Example

a = c + d; // this is a simple single line comment
/* however, this comment continues on more
than one line this is multiline comment */
assign y = temp_reg;
assign x=ABC /* plus its compliment*/ + ABC_

• Numbers

Number storage is defined as a number of bits, but values can be specified in binary, octal, decimal or hexadecimal.

Example

3’b001, a 3-bit number 
5’d30,    (=5’b11110)
16‘h5ED4, (=16’d24276)

reg [15:0] x = 16'h9678