--Program for Programmable Peripheral Intterface.
library IEEE;
use IEEE.std_logic_1164.all;
use IEEE.std_logic_unsigned.all;
use IEEE.std_logic_arith.all;

entity ppi is
	port (
		a0: in STD_LOGIC;
		a1: in STD_LOGIC;
		reset: in STD_LOGIC;
		csb: in STD_LOGIC;
		rdb: in STD_LOGIC;
		wrb: in STD_LOGIC;
		din: inout STD_LOGIC_vector(7 downto 0); 
		pa: inout STD_LOGIC_vector(7 downto 0);
		pb: inout STD_LOGIC_vector(7 downto 0);
		pcl: inout STD_LOGIC_vector(3 downto 0); 
		pcu: inout STD_LOGIC_vector(7 downto 4) 
	      );
end ppi;

architecture ppi_arch of ppi is
signal cwr:std_logic_vector(7 downto 0);
signal wrbu,rdbu,rdba,wrba,rdbcu,rdbcl,rdbb,wrbcl,wrbcu,wrbb:std_logic;
signal wa,xa,ya,za,wb,xb,yb,zb:std_logic_vector( 7 downto 0);
signal wcl,xcl,ycl,zcl:std_logic_vector( 3 downto 0);
signal wcu,xcu,ycu,zcu:std_logic_vector( 7 downto 4);
signal a :std_logic_vector(7 downto 0);
signal c :std_logic_vector(2 downto 0); 
begin 
process(a1,a0,rdb,wrb,csb,wrba,rdba,reset,wrbb,rdbb,rdbcl,wrbcl,rdbcu,wrbcu)
begin
wrbu<=wrb;
rdbu<=rdb;

if csb<='0' then 

-- ***** architecture ports_arch of portss *****
-- ****** PORT A STARTS ******



if(a1='0' and a0='0') then
	for i in 0 to 7 loop
		if(wrba='1' and reset='1')then
		   wa(i)<='Z';
		else 
		   wa(i)<=din(i);
		end if;
		if(reset='0') then
		   xa(i) <= wa(i);
		else
		   xa(i)<='0';
		end if;
		if(wrba='1'and reset='1') then
		   pa(i)<='Z';
		else
		   pa(i)<=xa(i);
		end if;
		if(rdba='1' and reset='1')then
		   ya(i)<='Z';
		else 
		   ya(i)<=pa(i);
		end if;
		if(reset='0')then
		   za(i)<=ya(i);
		else
		   za(i)<='0';
		end if;
		if(rdba='1' and reset='1')then
		   din(i)<='Z'; 
		else 
		   din(i)<=za(i);
		end if;
	end loop;
else
pa<="ZZZZZZZZ"; 

end if;

-- PORT A ENDS-

-- PORT B STARTS---

if(a1='0' and a0='1') then 

	for i in 0 to 7 loop
		if(wrbb='1' and reset='1')then
		   wb(i)<='Z';
		else
		   wb(i)<=din(i);
		end if;
		if(reset='0') then
		   xb(i)<=wb(i);
		else
		   xb(i)<='0';
		end if;
		if(wrbb='1'and reset='1')then
		   pb(i)<='Z';
		else
		   pb(i)<=xb(i);
		end if;
		if(rdbb='1' and reset='1')then
   		   yb(i)<='Z';
		else
		   yb(i)<=pb(i);
		end if;
		if(reset='0')then
		   zb(i)<=yb(i);
		else
		   zb(i)<='0';
		end if;
		if(rdbb='1' and reset='1')then
		   din(i)<='Z';
		else 
		   din(i)<=zb(i);
		end if;
	end loop;
else
pb<="ZZZZZZZZ";
end if;

-- PORT B ENDS--

-- PORT CL STARTS--


if (a1='1' and a0='0') then 
	for i in 0 to 3 loop
		if(wrbcl='1' and reset='1')then
		   wcl(i)<='Z';
		else
		   wcl(i)<=din(i);
		end if;
		if(reset='0') then
		   xcl(i)<=wcl(i);
		else
		   xcl(i)<='0';
		end if;
		if(wrbcl='1'and reset='1')then
		   pcl(i)<='Z';
		else 
		   pcl(i)<=xcl(i);
		end if;
		if(rdbcl='1' and reset='1')then
		   ycl(i)<='Z';
		else
		   ycl(i)<=pcl(i);
		end if;
		if(reset='0')then
		   zcl(i)<=ycl(i);
		else
		   zcl(i)<='0';
		end if;
		if(rdbcl='1' and reset='1')then
		   din(i)<='Z';
		else
		   din(i)<=zcl(i);
		end if;
	end loop;
else
pcl<="ZZZZ";
end if;



--PCL ENDS--
--PCU STARTS-- 


if(a1='1' and a0='0') then 
	for i in 4 to 7 loop 
		if(wrbcu='1' and reset='1')then
		   wcu(i)<='Z';
		else
		   wcu(i)<=din(i);
		end if;
		if(reset='0') then
		   xcu(i)<=wcu(i);
		else
		   xcu(i)<='0';
		end if;
		if(wrbcu='1'and reset='1')then
		   pcu(i)<='Z';
		else 
		   pcu(i)<=xcu(i);
		end if;
		if(rdbcu='1' and reset='1')then
		   ycu(i)<='Z';
		else
		   ycu(i)<=pcu(i);
		end if;
		if(reset='0')then
		   zcu(i)<=ycu(i);
		else
		   zcu(i)<='0';
		end if;
		if(rdbcu='1' and reset='1')then
		   din(i)<='Z';
		else
		   din(i)<=zcu(i);
		end if;
	end loop;
else
pcu<="ZZZZ";
pcl<="ZZZZ";
end if;


--PCU ENDS-- 
--MODE_0 STARTS--


if (a0='1' and a1='1' and wrb='0' and rdb='1')then
 
	case cwr is 
		when "10000000" =>rdba<='1';wrba<='0';rdbcu<='1'; wrbcu<='0';rdbb<='1';wrbb<='0'; rdbcl<='1';wrbcl<='0';
pa<=din; pb<=din; pcl<=din(3 downto 0);pcu<=din(7 downto 4);

when "10000001" =>rdba<='1';wrba<='0';rdbcu<='1';wrbcu<='0';rdbb<='1';wrbb<='0'; rdbcl<='0';wrbcl<='1';
pa<=din;pb<=din;din(3 downto 0)<=pcl;pcu<=din(7 downto 4);

when "10000010" =>rdba<='1';wrba<='0'; rdbcu<='1'; wrbcu<='0';rdbb<='0';wrbb<='1'; rdbcl<='1';wrbcl<='0';
pa<= din;din<=pb;pcl<=din(3 downto 0);pcu<=din(7 downto 4);

when "10000011" =>rdba<='1';wrba<='0';rdbcu<='0'; wrbcu<='1';rdbb<='0';wrbb<='1'; rdbcl<='1';wrbcl<='0';
pa<= din;din<=pb; din(3 downto 0)<=pcl;pcu<=din(7 downto 4);

when "10001000" =>rdba<='1';wrba<='0';rdbcu<='0';wrbcu<='1';rdbb<='1';wrbb<='0'; rdbcl<='1';wrbcl<='0';
din<=pa;din<=pb;pcl<=din(3 downto 0);din(7 downto 4)<=pcu;

when "10010010" =>rdba<='0';wrba<='1'; rdbcu<='1'; wrbcu<='0';rdbb<='1';wrbb<='0'; rdbcl<='1';wrbcl<='0';
din<=pa;din<=pb;pcl<=din(3 downto 0);pcu<=din(7 downto 4);
when others=>null;
end case; 
end if;



-- START BSR-MODE ---

if (a1='1' and a0='1')then 
	cwr<=din;
	if (rdbu='1' and wrbu='0' and csb='0' and reset='0') then

		if cwr(7)='0' then
		   c<=cwr(3) & cwr(2) & cwr(1);
	case c is
		when "000" => pcl(0)<=cwr(0);
		when others =>pcl(0)<=pcl(0);
	end case;
	case c is
		when "001" => pcl(1)<=cwr(0);
		when others =>pcl(1)<=pcl(1);
	end case;
	case c is
		when "010" => pcl(2)<=cwr(0);
		when others =>pcl(2)<=pcl(2);
	end case;
	case c is
		when "011" => pcl(3)<=cwr(0);
		when others =>pcl(3)<=pcl(3);
	end case;
	case c is
		when "100" => pcu(4)<=cwr(0);
		when others =>pcu(4)<=pcu(4);
	end case;
	case c is
		when "101" => pcu(5)<=cwr(0);
		when others =>pcu(5)<=pcu(5);
	end case;
	case c is
		when "110" => pcu(6)<=cwr(0);
		when others =>pcu(6)<=pcu(6);
	end case;
	case c is
		when "111" => pcu(7)<=cwr(0);
		when others =>pcu(7)<=pcu(7);
	end case;

		end if;
	end if;
end if;
else
din<="ZZZZZZZZ" ; 
end if; 
end process; 
end ppi_arch;