-- 7-Segment Decoder with active low outputs, Lamp Test, Blanking, and Ripple Blanking

LIBRARY ieee;
USE ieee.std_logic_1164.ALL;

ENTITY seven_seg IS
	PORT(
		Ain, Bin, Cin, Din, nLT, nBI,  nRBI    	: IN	STD_LOGIC; 
		na, nb, nc, nd, ne, nf, ng, nRBO		: OUT	STD_LOGIC);
END seven_seg;

ARCHITECTURE decoder OF seven_seg IS
	SIGNAL input: STD_LOGIC_VECTOR (3 DOWNTO 0);  
	SIGNAL output: STD_LOGIC_VECTOR (6 DOWNTO 0);	
BEGIN
-- Concurrent signal assignment 
input (0) <= Ain;
input (1) <= Bin;
input (2) <= Cin; 
input (3) <= Din;	

display:
PROCESS (input, nRBI, nBI, nLT)
BEGIN	
	--  If Statement
		IF (input = "0000" and nRBI ='0') THEN  -- Blank leading 0
			output	<=	"1111111";									
			nRBO	<=	'0';
		ELSIF (input = "0000" and nRBI = '1') THEN -- display 0
			output	<=	"0000001";		
			nRBO	<=	'1';
		ELSE
			CASE input IS
				WHEN "0001"	=>	output	<=	"1001111"; --display 1
				WHEN "0010"	=>	output	<=	"0010010"; --display 2
				WHEN "0011"	=>	output	<=	"0000110"; --display 3
				WHEN "0100"	=>	output	<=	"1001100"; --display 4
				WHEN "0101"	=>	output	<=	"0100100"; --display 5
				WHEN "0110"	=>	output	<=	"0100000"; --display 6	
				WHEN "0111"	=>	output	<=	"0001111"; --display 7
				WHEN "1000"	=>	output	<=	"0000000"; --display 8
				WHEN "1001"	=>	output	<=	"0000100"; --display 9
				WHEN "1010"	=>	output	<=	"0001000"; --display A
				WHEN "1011"	=>	output	<=	"1100000"; --display B
				WHEN "1100"	=>	output	<=	"0110001"; --display C
				WHEN "1101"	=>	output	<=	"1000010"; --display D
				WHEN "1110"	=>	output	<=	"0110000"; --display E
				WHEN "1111"	=>	output	<=	"0111000"; --display F
				WHEN others 	=>	output	<=	"1111111"; --blank 				
				END CASE;
			nRBO	<=	'1';
			END IF;
		IF (nBI='0') THEN	-- override DCBA and blank the display
			output	<=	"1111111";
			END IF;
		IF (nLT='0') THEN	-- override DCBA and lamp test. 
			output	<=	"0000000";
			END IF;

	na	<=	output(6);
	nb	<=	output(5);
	nc	<=	output(4);
	nd	<=	output(3);
	ne	<=	output(2);
	nf	<=	output(1);
	ng	<=	output(0);
END PROCESS display;
END decoder;