n位加法器.vhd

含有各类寄存器

--n-bit Adder using the Generate Statement
ENTITY addn IS
    GENERIC(n : POSITIVE := 3); --no. of bits less one
    PORT(addend, augend : IN BIT_VECTOR(0 TO n);
               carry_in : IN BIT; carry_out, overflow : OUT BIT;
                    sum : OUT BIT_VECTOR(0 TO n));
END addn;
ARCHITECTURE generated OF addn IS
SIGNAL carries : BIT_VECTOR(0 TO n);
BEGIN
addgen : FOR i IN addend'RANGE
         GENERATE
lsadder : IF i = 0 GENERATE
             sum(i) <= addend(i) XOR augend(i) XOR carry_in;
         carries(i) <= (addend(i) AND augend(i)) OR
         (addend(i) AND carry_in) OR
         (carry_in AND augend(i));
END GENERATE;
otheradder : IF i /= 0 GENERATE
               sum(i) <= addend(i) XOR augend(i) XOR carries(i-1);
           carries(i) <= (addend(i) AND augend(i)) OR
         (addend(i) AND carries(i-1)) OR
         (carries(i-1) AND augend(i));
END GENERATE;
END GENERATE;
         carry_out <= carries(n);
         overflow <= carries(n-1) XOR carries(n);
END generated;