On Wed, 28 May 2008 14:40:02 +0100, Rob <Rob@[EMAIL PROTECTED]
> wrote:
>>> ... if some_unsigned(31 downto 26) = "100111" then ...
>> How is data_bus declared? If it is std_logic_vector, this looks good
>> to me. The error message is saying that it can't find a version of
>> '=' that uses the two operand types and produces a boolean which is
>> required by the IF. Did you include the libraries?
>
>It is declared as unsigned...so in this case I cant compare bitwise I
>assume. But I could cast it to std_logic_vector, couldnt I?
I suspect the problem is that you're using the std_logic_arith
package rather than numeric_std.
std_logic_arith has overloads for unsigned=unsigned and also for
unsigned=signed. Consequently, the type of your "100111" is
ambiguous - although you aren't getting the right error message
for that - and the compiler should indeed choke on it. The
properly-standardised numeric_std package does not have an
unsigned=signed overload, so there's no ambiguity.
Fixes - ah, so many choices...
(1) cast to std_logic_vector as you suggest;
(2) type-qualify the constant as unsigned (NOTE the apostrophe):
if some_unsigned(31 downto 26) = unsigned'("100111") then...
(3) use numeric_std in preference to std_logic_arith;
(4) use an ordinary integer literal for the comparison:
if some_unsigned(31 downto 26) = 39 then ...
if some_unsigned(31 downto 26) = 2#100111# then ...
hth
--
Jonathan Bromley, Consultant
DOULOS - Developing Design Know-how
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Doulos Ltd., 22 Market Place, Ringwood, BH24 1AW, UK
jonathan.bromley@[EMAIL PROTECTED]
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