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ModelSim SE User's Manual - Electrical and Computer Engineering

ModelSim SE User's Manual - Electrical and Computer Engineering

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Compiling VHDL files UM-77<br />

bit string literals<br />

In VHDL-87 bit string literals are of type bit_vector. In VHDL-93 they can also be of<br />

type STRING or STD_LOGIC_VECTOR. This implies that some expressions that are<br />

unambiguous in VHDL-87 now become ambiguous is VHDL-93. A typical error<br />

message is:<br />

** Error: bit_string_literal.vhd(5): Subprogram '=' is ambiguous. Suitable<br />

definitions exist in packages 'std_logic_1164' <strong>and</strong> 'st<strong>and</strong>ard'.<br />

In VHDL-87 when using individual subelement association in an association list,<br />

associating individual sub-elements with NULL is discouraged. In VHDL-93 such<br />

association is forbidden. A typical message is:<br />

"Formal '' must not be associated with OPEN when subelements are<br />

associated individually."<br />

<strong>ModelSim</strong> <strong>SE</strong> User’s <strong>Manual</strong>

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