Hamster FPGA tutorials. 4 bit adder, does this look right?

[mubase 0]

Hi all. I recieved my LogicStart today so as I have a few hours spare I thought I'd get cracking wth Hamster's PDF of tutorials and info.

I've just finished making a 4 bit adder using the swithces and LEDs of the board and would like to know if my code looks right. It seems to work.. From right to left, the switches in 2 groups of 4 seem to add up all the way to 15.

The code is here:

entity switches_leds is   Port ( switches : in STD_LOGIC_VECTOR(7 downto 0);LEDs : out STD_LOGIC_VECTOR(7 downto 0));end switches_leds;architecture Behavioral of switches_leds issignal x		: STD_LOGIC_VECTOR (3 downto 0);signal y		: STD_LOGIC_VECTOR (3 downto 0);signal carry : STD_LOGIC_VECTOR (3 downto 0);signal result : STD_LOGIC_VECTOR (4 downto 0);beginLEDs <= "000" & result;x <= switches (3 downto 0);y <= switches ( 7 downto 4 );result(0) <= x(0) XOR y(0);carry(0) <= x(0) AND y(0);result(1) <= x(1) XOR y(1) XOR carry(0);carry(1) <= (x(1) AND y(1)) OR (carry(0) AND x(1)) OR (carry(0) AND y(1));result(2) <= x(2) XOR y(2) XOR carry(1);carry(2) <= (x(2) AND y(2)) OR (carry(1) AND x(2)) OR (carry(1) AND y(2));result(3) <= x(3) XOR y(3) XOR carry(2);carry(3) <= (x(3) AND y(3)) OR (carry(2) AND x(3)) OR (carry(2) AND y(3));--result(4) <= x(4) XOR y(4) XOR carry(3);--carry(4) <= x(4) AND y(4) OR (carry(3) AND x(4)) OR (carry(3) AND y(4));end Behavioral;

 

I have some boolean experience having gone to college to do an access course in Audio electronics/music technology and being thrown in the deep end of boolean logic. :s

At the time all of us in the class were wondering where it all fitted in with Audio systems electronics but I am glad of it now.

If someone could verify this for me I'd be much appreciative.

All the best,

Steve.

 

[alvieboy 25]

You can try this in a different way, like explained on my basic tutorial:

 

http://alvie.com/zpuino/vhdl1.html

 

You'll have a 4-bit adder on the third example.

 

Alvie

[hamster 47]

Steve! Looking good... you could just assign result(4) the value of carry(4)., and then you could add all the way to 30!

[mubase 0]

Hi! thats great to hear! I'll try the suggestions and then try and tackle the subtractor...:s