|
VHDL Tutorial |
VHDL lexical elements and syntax | ||
|
Introduction Fundamental concepts Modelling concepts Elements of behaviour Elements of structure Analysis elaboration Lexical elements Identifiers Numbers Characters and strings Syntax descriptions Constants and variables Scalar type Integer types Floating point types Time type Enumeration types Character types Boolean type Bits type Standard logic Sequential statements Case statements Loop and exit statements Assertion statements Array types & array operations Architecture bodies Entity declarations Behavioral descriptions Wait statements Delta delays Process statements Conditional signal assignment Selected signal assigment Structural descriptions Library and library clauses Procedures Procedure parameters Signal parameters Default values Unconstrained array parameter Functions Package declarations and bodies Subprograms in package Use clauses Resolved signals and subtypes Resolved signals and ports Parameterizing behavior Parameterizing structure
|
. Lexical Elements and Syntax
When we learn a new language, we need to learn how to write the basic elements, such as numbers and identifiers. We also need to learn the syntax, that is, the gram- mar rules governing how we form language constructs. We will briefly describe the lexical elements and our notation for the grammar rules, and then start to introduce langauge features. VHDL uses characters in the ISO 8859 Latin-1 8-bit character set. This includes uppercase and lowercase letters (including letters with diacritical marks, such as ‘à’, ‘ä’ and so forth), digits 0 to 9, punctuation and other special characters.
Want To have highly paid VLSI jobs ?? then you may contact at
Contact : webmaster@freehost7com Comments
When we are writing a hardware model in VHDL, it is important to annotate the code with comments. A VHDL model consists of a number of lines of text. A comment can be added to a line by writing two dashes together, followed by the comment text. For example:
… a line of VHDL description … – – a descriptive comment
The comment extends from the two dashes to the end of the line and may include any text we wish, since it is not formally part of the VHDL model. The code of a model can include blank lines and lines that only contain comments, starting with two dashes. We can write long comments on successive lines, each starting with two dashes, for example:
– – The following code models – – the control section of the system … some VHDL code …
|