EE295 - ASIC Design With VHDL Class - Fall 1998

Aliases

Assignment:

• Read Ch 9

• Aliases
• Aliases for Data Objects
• Aliases for Non-Data Objects

Aliases

Aliases for Data Objects

• Variables, Constants, Signals May Have Aliases
• Sub-Elements of Composite Types May be Selected
• Slice of an Array
• Field of a Record
• Alias can be of an Alias
• IEEE-87 Declaration Syntax
Alias Alias_Name : Sub_Type_Indication Is Object_Name ;
• IEEE-93 Declaration Syntax
• Sub-Type Indication is Optional Alias alias_name |: Sub_type_indication | Is Name ;
• Example
Subtype dlx_word is std_logic_vector(0 to 31); Signal IR : dlx_word; Alias instruction_field Is IR ( 0 to 5 ); Alias source_register Is IR ( 6 to 11 );

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IEEE-93 Aliases for Non-Data Objects

• Wider Application of Alias Concept in Updated Standard
• Types
• SubPrograms
• Packages
• Entities
• Declaration Syntax

Alias ( identifier | character_literal | operator_symbol ) Is name [ signature ] ;
• Example

Alias "+" Is "or" [ bit, bit return bit ] ;
• Creates Operator "+" Defined for Type Bit