I am trying to make an up/down counter on a Basys board. But I have some issues I can't figure out.

My code:

library IEEE;

entity counter is
  Port (
    clock       : in  STD_LOGIC;
    clock_osc   : in  STD_LOGIC;
    reset       : in  STD_LOGIC;
    count_start : in  STD_LOGIC;
    count_out   : out STD_LOGIC_VECTOR (3 downto 0);
    AN1         : out STD_LOGIC;
    AN2         : out STD_LOGIC;
    AN3         : out STD_LOGIC;
    AN4         : out STD_LOGIC
end counter;

architecture Behavioral of counter is
  signal count : std_logic_vector (3 downto 0);
  signal count2 : std_logic_vector (3 downto 0);

  countupdown: process (clock, reset, count_start)
    if (reset = '0') then
      count <= "0000";
      count2 <= "0000";
    elsif (clock='1' and clock'event) then
      if (count_start = '0') then
        count <= count + 1;
        count2 <= count2 - 1;
      end if;
    end if;
  end process;

  count_out<= count when (clock_osc = '1') else count2;
  AN1<='0' when (clock_osc='1') else '1';
  AN2<='0' when (clock_osc='1') else '1';
  AN3<='1' when (clock_osc='1') else '0';
  AN4<='1' when (clock_osc='1') else '0' ;

end Behavioral;

The errors:

ERROR:HDLParsers:808 - "C:/Users/sana4/Desktop/uni/Digital Design/Counter3/counter.vhd" Line 75. + can not have such operands in this context.
ERROR:HDLParsers:808 - "C:/Users/sana4/Desktop/uni/Digital Design/Counter3/counter.vhd" Line 79. - can not have such operands in this context.
  • 1
    \$\begingroup\$ Please format your code properly, eliminate the extra blank lines, and tell us which lines are line 75 and 79. \$\endgroup\$ – Joe Hass Apr 24 '14 at 10:38

I've taken the liberty of cleaning up your listing and formatting it for compactness and readability, so I've undoubtedly messed up the line numbering.

The specific errors you're getting are caused by the fact that you can't do arithmetic on std_logic_vector, e.g., to increment and decrement your counters. At a minimum, you need to include the library ieee.numeric_std in order to allow this. See the answers to this question for additional details.


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