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[guylewis]

What does the aspostrophe mean between vector'(

period_h_register <= std_logic_vector'("0000000000000001")


Thanks for any help

lewis

[jeppe]

You will find the same structure with for instance

if Clk'event and Clk='1' then .....

if Rising_Edge(Clk) then .... -- alternative version

I believe its same kind of type conversion between std_logic and std_ulogic but I never used it.

Jeppe

[guylewis]

Originally Posted by jeppe

You will find the same structure with for instance

if Clk'event and Clk='1' then .....

if Rising_Edge(Clk) then .... -- alternative version

I believe its same kind of type conversion between std_logic and std_ulogic but I never used it.

Jeppe

Thanks Jeppe

Someone from another forum sent me this answer.

"Qualified expressions" may be used to explicitly identify the type, and possibly the subtype, of an expression. Such qualification is a "hint" to the compiler, informing it as to the desired interpretation of the expression being qualified. Hence, such qualification is legal only if the expression can be legally interpreted as a value of the qualifying type. In contrast to type conversion, no information loss can occur.

The syntax of a qualified expression is similar to the syntax of a type conversion. The difference is that a "tick" (the ''' character) is inserted between the type name and the parentheses surrounding the expression, as shown in the next example:

-- note, both enumeration type declarations have some common
-- enumeration items
type color1 is (violet, blue, green, yellow, red);
type color2 is (black, blue, green, red);

-- this array type has an index type "color1". Without
-- using type qualification this example will not compile
-- because the compiler cannot determine the type
-- of "blue" (might be "color1" or "color2").
type a1 is array(color1'(blue) to color1'(red));

-- this array type has an index type "color2". Without
-- using type qualification this example will not compile
type a2 is array(color2'(blue) to color2'(red));

[jeppe]

Thanks for question and answer - I learnt something new