binaryvhdlbcd

Converting 8 bit binary to BCD value

I have spent countless hours on this and I just finally decided I really need some help..so here I am.

Basically what I am doing is taking an 8 bit input from an ADC and then converting this value to BCD to display on a seven segment board. SO here is my code so far:

Library IEEE ;
use IEEE.STD_LOGIC_1164.ALL;
use ieee.numeric_std.all;
use IEEE.std_logic_unsigned.all;

entity Voltage_LUT is
  Port ( scaled_value : in  unsigned(7 downto 0);
         true_value : out  STD_LOGIC_VECTOR (15 downto 0)
  );
end Voltage_LUT;

architecture Behavioral of Voltage_LUT is

  function  divide  (a : UNSIGNED; b : UNSIGNED) return unsigned is
    variable a1 : unsigned(a'length-1 downto 0):=a;
    variable b1 : unsigned(b'length-1 downto 0):=b;
    variable p1 : unsigned(b'length downto 0):= (others => '0');
    variable i : integer:=0;
  begin
    for i in 0 to b'length-1 loop
      p1(b'length-1 downto 1) := p1(b'length-2 downto 0);
      p1(0) := a1(a'length-1);
      a1(a'length-1 downto 1) := a1(a'length-2 downto 0);
      p1 := p1-b1;
      if(p1(b'length-1) ='1') then
        a1(0) :='0';
        p1 := p1+b1;
      else
        a1(0) :='1';
      end if;
    end loop;
    return a1;
  end divide;

  signal  adj: unsigned(7 downto -2);    --adjusted to max 90
  signal  max_value: unsigned(7 downto 0):= "11111111" ;    --adjusted to max 90
  signal  MSB_int: integer;   -- integer form of MSB
  signal  LSB_int: integer;    --integer form of LSB
  signal  adj2: unsigned(15 downto 0);    --converted from adjusted integer to binary
  signal  LSB: STD_LOGIC_VECTOR (3 downto 0);    --BCD for LSB
  signal  MSB: STD_LOGIC_VECTOR (3 downto 0);    --BCD for MSB
  signal  OFF: STD_LOGIC_VECTOR (3 downto 0):="1010";    --defined to be segment OFF
  signal  V: STD_LOGIC_VECTOR (3 downto 0):="1011";    --defined to be letter V

begin

  adj <= divide ( scaled_value , max_value );
  adj2 <= adj* "00001001" ;

end Behavioral;

Essentially what I am doing is taking an 8 bit value from the ADC then expressing it as a fraction of the max value (which is 9) and then I have to convert this to BCD... but when I am running this code I am getting an error stating:

Line 38: Index value <-2> is out of range [0:2147483647] of array

I need the answer of the division to be a binary number (with decimals eg 11001.110) so that it would be accurate when I multiply it by 9...

Solution

  • The offending line is:

    signal  adj: unsigned(7 downto -2);

    The type unsigned does not support negative ranges. If you want to treat your result as a fixed-point value with a fractional component, you have a couple choices, including: