DIY Electronics Projects and Tutorials: XC95108 Two-Digit BCD to 7-Segment Display VHDL

In this VHDL example, I use an XC95108 CPLD to read and convert two digits BCD variable to two distinct 7-Segment display. The input is an active low push button without de-bouncing or delay circuit. So the input press counting is unstable. I create two BCD variable to hold the 1'S and the 10's values.

Circuit Testing on the XC95108 Prototype Board

The 7-Segment display is a 0.56 Inch individual digit command cathode type. This VHDL code create a digital counter that counts up to 99 before its rolls down to 0.

--XC95108 Two-Digit 7-Segment Counter With Pusth Button
--Circuit Design with VHDL
LIBRARY IEEE;
USE IEEE.STD_LOGIC_1164.ALL;
 
ENTITY counter IS
	PORT(	CLK,RESET: IN STD_LOGIC;
			DIGIT1, DIGIT2: OUT STD_LOGIC_VECTOR(7 DOWNTO 0)
			);
END counter;
 
ARCHITECTURE counter of counter IS
BEGIN
	PROCESS(CLK,RESET)
		VARIABLE temp1: INTEGER RANGE 0 TO 10;
		VARIABLE temp2: INTEGER RANGE 0 TO 10;
	BEGIN
		if(RESET='1') then temp1:=0; temp2:=0;
		elsif(CLK'EVENT AND CLK='0') then
			temp1:=temp1+1;
			if(temp1>=10) then temp1:=0; temp2:=temp2+1;
				if(temp2>=10) then temp2:=0; end if;
			end if;
		end if;
		--BCD TO SSD Conversion--
		--DIGIT 1--
		CASE temp1 IS
			WHEN 0	=> DIGIT1<=x"3F";
			WHEN 1	=> DIGIT1<=x"06";
			WHEN 2	=> DIGIT1<=x"5B";
			WHEN 3	=> DIGIT1<=x"4F";
			WHEN 4	=> DIGIT1<=x"66";
			WHEN 5	=> DIGIT1<=x"6D";
			WHEN 6	=> DIGIT1<=x"7D";
			WHEN 7	=> DIGIT1<=x"07";
			WHEN 8	=> DIGIT1<=x"7F";
			WHEN 9 	=> DIGIT1<=x"6F";
			WHEN	OTHERS	=> NULL;
		END CASE;
		--DIGIT 2--
		CASE temp2 IS
			WHEN 0	=> DIGIT2<=x"3F";
			WHEN 1	=> DIGIT2<=x"06";
			WHEN 2	=> DIGIT2<=x"5B";
			WHEN 3	=> DIGIT2<=x"4F";
			WHEN 4	=> DIGIT2<=x"66";
			WHEN 5	=> DIGIT2<=x"6D";
			WHEN 6	=> DIGIT2<=x"7D";
			WHEN 7	=> DIGIT2<=x"07";
			WHEN 8	=> DIGIT2<=x"7F";
			WHEN 9 	=> DIGIT2<=x"06";
			WHEN	OTHERS	=> NULL;
		END CASE;
	END PROCESS;
END counter;

I use VHDL sequential code to make this circuit. It contains IF and CASE statements. I got this sample VHDL code from "Circuit Design with VHDL, Volnei A. Prdroni".

The XC95108, switches and 7-Segment display are connected as follow.

#PACE: Start of Constraints generated by PACE
#PACE: Start of PACE I/O Pin Assignments
NET "CLK" LOC = "P53" ;
NET "DIGIT1<7>" LOC = "P37" ;
NET "DIGIT1<6>" LOC = "P35" ;
NET "DIGIT1<5>" LOC = "P21" ;
NET "DIGIT1<4>" LOC = "P33" ;
NET "DIGIT1<3>" LOC = "P34" ;
NET "DIGIT1<2>" LOC = "P36" ;
NET "DIGIT1<1>" LOC = "P24" ;
NET "DIGIT1<0>" LOC = "P23" ;
NET "DIGIT2<7>" LOC = "P32" ;
NET "DIGIT2<6>" LOC = "P18" ;
NET "DIGIT2<5>" LOC = "P17" ;
NET "DIGIT2<4>" LOC = "P26" ;
NET "DIGIT2<3>" LOC = "P25" ;
NET "DIGIT2<2>" LOC = "P31" ;
NET "DIGIT2<1>" LOC = "P20" ;
NET "DIGIT2<0>" LOC = "P19" ;
NET "RESET" LOC = "P48" ;
#PACE: Start of PACE Area Constraints
#PACE: Start of PACE Prohibit Constraints
#PACE: End of Constraints generated by PACE

The two-digit 7-Segment display schematic is shown below.