Range
A range specifies a range of values belonging to an integer, floating, physical
or enumeration type. A static range is one whose bounds can be calculated
during compilation or elaboration.
Syntax
{either}
Expression to Expression
Expression downto Expression
Name'RANGE {name of an array or array type}
Name'REVERSE_RANGE
DataType {enumeration or integer type}
Placement
PACKAGE Pack IS
... 
END PACKAGE Pack;
|
PACKAGE BODY Pack IS
...
END PACKAGE BODY Pack;
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Blk:BLOCK
...
BEGIN
...
END BLOCK Blk;
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ENTITY Ent IS
...
BEGIN
...
END ENTITY Ent;
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ARCHITECTURE Arc OF Ent IS
...
BEGIN
...
END ARCHITECTURE Arc;
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CONFIGURATION Conf OF Ent IS
...
END CONFIGURATION Conf;
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Proc:PROCESS(...)
...
BEGIN
...
END PROCESS Proc;
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PROCEDURE P(...) IS
...
BEGIN
...
END PROCEDURE P;
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FUNCTION F(...) RETURN Tp IS
...
BEGIN
...
END FUNCTION F;
|
Rules
The values of the Expressions must be consistent with the direction of the
range. E.g. 0 downto 7 is a null range, of length 0.
Tips
Any form of range can be used in a for loop or an index constraint.
Use the 'RANGE form of range in preference to Expression to Expression
where possible, as this often makes the code easier to maintain.
Example
subtype INT is INTEGER range 0 to 7;
subtype V1 is STD_LOGIC_VECTOR(INT);
subtype V2 is INTEGER range V1'REVERSE_RANGE;
...
for I in V2 range 3 downto 0 loop
...
See Also
Data Type, Subtype, Integer, Floating, Attribute Name
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