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LED interfacing with Spartan3 FPGA Development Kit

It’s always interesting to glow LED’s on any piece of hardware. What you can do with those LED’s? You can Blink them, you can Scroll from Left to Right and Right to Left, you can Count them , you can display any logic output which can be ‘0’ or ‘1’.

Spartan3 FPGA Development Kitgot array of 10 LED’s to perform all the above mentioned operations. We are here to explore more on how to perform binary counter with those LED’s.

Now we are going to construct 16- bit Binary Counter. The 16-bit Synchronous Binary Counter counts sequentially on positive edge of every clock cycle.

Schematics to interface LED with Spartan3 FPGA Development Kit





LED Placement in Spartan3 FPGA Development Kit





VHDL Code for 10-Bit Binary Counter

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_unsigned.all;

entity counter is port(Clock, PRE : in std_logic;

Q : out std_logic_vector(15 downto 0));

end counter;

architecture bhv of counter is signal tmp: std_logic_vector(15 downto 0);

begin process (Clock, PRE) begin if (PRE='1') then tmp <= (others => '0');

elsif (Clock'event and Clock='1')

then tmp <= tmp + 1;

end if;

end process;

Q <= tmp; end bhv;

From the above code, we will get counter running at 50MHz Speed which means it will count at the speed of 20 ns. You can’t visibly see the output of Counter with LED’s at 20 ns. Instead you can check them in simulation.

To make the count visible we are introducing 33 bit clock divider and assign the last 16 MSB bits to the output LED’s. This gives the result of binary count at every 1s.

library ieee;

use ieee.std_logic_1164.all;

use ieee.std_logic_unsigned.all;

entity counter is port(Clock, PRE : in std_logic;

Q : out std_logic_vector(15 downto 0));

end counter;

architecture arch of counter is signal tmp:

std_logic_vector(32 downto 0);

begin process (Clock, PRE) begin if (PRE='1') then tmp <= (others => '0');

elsif (Clock'event and Clock='1')

then tmp <= tmp + 1;

end if;

end process;

Q <= tmp(32 downto 17);

end arch;

Pin Assignment for Spartan3 Stick Board.

NET "Q[0]" LOC = P36;

NET "Q[1]" LOC = P37;

NET "Q[2]" LOC = P39;

NET "Q[3]" LOC = P40;

NET "Q[4]" LOC = P42;

NET "Q[5]" LOC = P43;

NET "Q[6]" LOC = P44;

NET "Q[7]" LOC = P45;

NET "Q[8]" LOC = P62;

NET "Q[9]" LOC = P63;

NET "Q[10]" LOC = P64;

NET "Q[11]" LOC = P65;

NET "Q[12]" LOC = P67;

NET "Q[13]" LOC = P68;

NET "Q[14]" LOC = P71;

NET "Q[15]" LOC = P72;

NET "Clock" LOC = P181;

NET "PRE" LOC = P46;