Slide 47 of 93
Scalar objects can hold only one data value at a time. A simple example is the integer data type. Variables and signals of type integer can only be assigned integers within a simulator-specific range, although the VHDL standard imposes a minimum range.
In the above example, the first two variable assignments are valid since they assign integers to variables of type integer. The last variable assignment is illegal because it attempts to assign a real number value to a variable of type integer.