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VHDL Tutorial |
Identifiers | ||
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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
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. Identifiers
Identifiers are used to name items in a VHDL model. An identifier
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Contact : webmaster@freehost7com • may only contain alphabetic letters (‘A’ to ‘Z’ and ‘a’ to ‘z’), decimal digits (‘0’ to ‘9’) and the underline character (‘_’);
• must start with an alphabetic letter;
• may not end with an underline character; and
• may not include two successive underline characters.
Case of letters is not significant. Some examples of valid basic identifiers are
A X0 counter Next_Value generate_read_cycle
Some examples of invalid basic identifiers are
last@value – – contains an illegal character for an identifier 5bit_counter – – starts with a nonalphabetic character _A0 – – starts with an underline A0_ – – ends with an underline clock__pulse – – two successive underlines
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