8 bit Mod VHDL question

[Jorge Jesse Cantu]

Hello fellow engineers/enthusiasts! I wrote the following program for an 8-bit modula N-bit counter, where N was a specified constant. I had to alter it a little bit due to my friend helping me, but what he altered I am confused about.

My question is, why does he assign my cout to din within my for loop? Din isn't counting, so I am confused on what sort of value din would have and/or assign to cout.

Also I'd be interested to see what a timing diagram for the din input and cout output would look like, but if you guys do not feel like drawing one up for me that is fine, I just want to get rid of my confusion.

Here is my code:

----------------------------------------------------------------------------------
-- Company: 
-- Engineer: 
----------------------------------------------------------------------------------
library IEEE;
use IEEE.STD_LOGIC_1164.ALL;

-- Uncomment the following library declaration if using
-- arithmetic functions with Signed or Unsigned values
--use IEEE.NUMERIC_STD.ALL;

-- Uncomment the following library declaration if instantiating
-- any Xilinx primitives in this code.
--library UNISIM;
--use UNISIM.VComponents.all;

entity nmod is
		port( clear: in std_logic;
				load:  in std_logic;
				arst_l: in std_logic;	--make it active low
				clk:	 in std_logic;
				din:	 in std_logic_vector(7 downto 0);
				count: out std_logic_vector(7 downto 0)
				);
end nmod;

architecture Behavioral of nmod is
constant N: std_logic_vector(7 downto 0) := X"C0";
signal cout: std_logic_vector(7 downto 0);
signal arst: std_logic;
signal dain: std_logic;

begin
count <= cout;		--output signal, output on left side
arst <= arst_l;	--input signal, input on right side
process(clk, arst)
begin
	if(arst = '1')then
		cout <= '0';
	elsif(clk'event and clk = '1')then
		if(clear = '1' or cout = 'N') then
		     cout <= din;
		else
		     cout <= cout +1;
		end if;
	end if;
end process;
end Behavioral;

 

[ads-ee]

Your "friend" isn't helping you out, with that change.

if (clear = '1' or cout = 'N') then

should be N without the 's.

Now if your friend meant to have the value of din load the counter to change the modulus then that would work, but I would instead make the N value into an input port and load that into the cout and decrement cout...reloading the N value when cout reaches X"00". Doing that will be a reduction NOR operation instead of an 8-bit compare operation.

Regards