See Also

The decoder.tdf file shown below is a 2-bit-to-4-bit decoder. It converts two binary code inputs into a "one-hot" code.

SUBDESIGN decoder
(
   code[1..0]	: INPUT;
   out[3..0]	: OUTPUT;
)
BEGIN
   CASE code[] IS
      WHEN 0 => out[] = B"0001";
      WHEN 1 => out[] = B"0010";
      WHEN 2 => out[] = B"0100";
      WHEN 3 => out[] = B"1000";
   END CASE;
END;

In this example, the input group code[1..0] has the value 0, 1, 2, or 3. The equation following the appropriate => symbol in the Case Statement is activated. For example, if code[] is 1, out1 is set to B"0010". Since the values of the expression are all different, only one WHEN clause can be active at one time.

Back to Top