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Homework Help: VHDL syntax error

  1. Mar 1, 2010 #1
    1. The problem statement, all variables and given/known data
    Creating an Up/Down counter with an output for both units and tens. (which can then be displayed on 7 segnment displays)

    2. Relevant equations

    3. The attempt at a solution

    Code (Text):
    library ieee;
    use ieee.std_logic_1164.all;
    use ieee.std_logic_arith.all;
    use ieee.std_logic_unsigned.all;

    entity UpDownCount is
      port(Clk, UpDown, reset: in std_logic;
      unit, tens: out std_logic_vector(3 downto 0)
    End UpDownCount;

    Architecture behv2 of UpDownCount is
    signal units1, tens1: unsigned(3 downto 0);
      process(UpDown, Clk, reset)
      variable CountUnits, CountTens : unsigned (3 downto 0);
      if (Clk'event and UpDown='1') then
         ****if CountUnits ='1111' then
          CountTens := CountTens + '1';
         ****CountUnits := CountUnits + '1';  
        end if;
      elsif (Clk'event and UpDown='0') then
        if CountUnits = '0000' then
          CountTens := CountTens - '1';
        else CountUnits := CountUnits - '1';
      end if;
    end if;
      end process
    end architecture
    The two lines with the stars are the ones where there are errors apparently. For the first one it says there is a syntax error near " ' ", and the second one it says it is expecting an "end" near "elseif". So I'm thinking is there a problem with my if-then statements? Do I need to use parenthesis to wrap the code thats included in the then part? I know its probably something quite simple, but I can't figure it out.
  2. jcsd
  3. Mar 1, 2010 #2


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    Homework Helper

    I've got very limited experience with VHDL (and don't have a simulator installed), but rather than CountUnits = '1111', try using CountUnits = "1111". Same goes for CountUnits ='0000'. Did this help?
  4. Mar 1, 2010 #3
    It did indeed, I forgot that youe need to use " when dealing with 0000 instead of just 0 etc.
    Thank you! There's also a ton of other mistakes in there, but I cleared them up too.
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