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Altera_Forum's avatar
Altera_Forum
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15 years ago

question about arithmetic operator '+'

Every time I try following code, there is a error saying that "Error (10327): VHDL error at Arithmetic.vhd(35): can't determine definition of operator ""+"" -- found 0 possible definitions", Can anyo...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
15 years ago

You get the error, because you are using unsuitable data types and incompatible libraries.

There are two possible ways:

- You can refer to the legacy non-IEEE STD_LOGIC_UNSIGNED library. But then you have to import STD_LOGIC_ARITH instead of NUMERIC_STD. bit_vector has to be changed to std_logic_vector in addition

- You can use correct VHDL types and the official IEEE.NUMERIC_STD library. The involved signals should be defined as unsigned in this case.

As a side remark, the inplemented left-shift can be simply written as 

var9 <= var3 & '0';

without involving numeric types.