tailieunhanh - Basic Concepts part 1

[ Team LiB ] Lexical Conventions The basic lexical conventions used by Verilog HDL are similar to those in the C programming language. Verilog contains a stream of tokens. Tokens can be comments, delimiters, numbers, strings, identifiers, and keywords. | Team LiB Lexical Conventions The basic lexical conventions used by Verilog HDL are similar to those in the C programming language. Verilog contains a stream of tokens. Tokens can be comments delimiters numbers strings identifiers and keywords. Verilog HDL is a case-sensitive language. All keywords are in lowercase. Whitespace Blank spaces b tabs t and newlines n comprise the whitespace. Whitespace is ignored by Verilog except when it separates tokens. Whitespace is not ignored in strings. Comments Comments can be inserted in the code for readability and documentation. There are two ways to write comments. A one-line comment starts with . Verilog skips from that point to the end of line. A multiple-line comment starts with and ends with . Multiple-line comments cannot be nested. However one-line comments can be embedded in multiple-line comments. a b c This is a one-line comment This is a multiple line comment This is an illegal comment This is a legal comment Operators Operators are of three types unary binary and ternary. Unary operators precede the operand. Binary operators appear between two operands. Ternary operators have two separate operators that separate three operands. a b is a unary operator. b is the operand a b c is a binary operator. b and c are operands a b c d is a ternary operator. b c and d are operands Number Specification There are two types of number specification in Verilog sized and unsized. Sized numbers Sized numbers are represented as size base format number . size is written only in decimal and specifies the number of bits in the number. Legal base formats are decimal d or D hexadecimal h or H binary b or B and octal o or O . The number is specified as consecutive digits from 0 1 2 3 4 5 6 7 8 9 a b c d e f. Only a subset of these digits is legal for a particular base. Uppercase letters are legal for number specification. 4 b1111 This is a 4-bit binary number 12 habc This is a 12-bit hexadecimal number 16 d255

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