VHDL Programming

440 Appendix B: VHDL Reference Tables

Table B-2
Attribute Explanation Examples

T’BASE Returns the base type of NATURAL’BASE returns

datatype it is attached to INTEGER

T’LEFT Returns left value specified in INTEGER’LEFT is -2147483647

type declaration BIT’LEFT is ‘ 0 ’

T’RIGHT Returns right value specified INTEGER’RIGHT is 2147483647

in type declaration BIT’RIGHT is ‘ 1 ’

T’HIGH Returns largest value specified TYPE bit8 is 255 downto 0

in declaration bit8’HIGH is 255

T’LOW Returns smallest value TYPE bit8 is 255 downto 0

specified in declaration bit8’LOW is 0

T’POS(X) Returns position number of TYPE color IS (red, green,

argument in type (first blue, orange);

position is 0) color’POS(green) is 1

T’VAL(X) Returns value in type at TYPE color IS (red, green,

specified position number blue, orange);

color’VAL(2) is blue

T’SUCC(X) Returns the successor to the TYPE color IS (red,

value passed in green, blue, orange);

color’SUCC(green) is

blue

T’PRED(X) Returns the predecessor to TYPE color IS (red, green,

the value passed in blue, orange);

color’PRED(blue) is green

T’LEFTOF(X) Returns the value to the left TYPE color IS (red, green,

of the value passed in blue, orange);

color’LEFTOF(green) is

red

T’RIGHTOF(X) Returns the value to the right TYPE color IS (red, green,

of the value passed in blue, orange);

color’RIGHTOF(blue) is

orange

Table B-3 lists all predefined attributes that return information about

array datatypes. The Nparameter for all attributes specifies to which par-

ticular range the attribute is being applied. This only makes sense for

multidimensional arrays. For single-dimensional arrays, the parameter

can be ignored. For more detailed information, see Chapter 6,“Predefined

Attributes.”