Digital Systems: Principles and Design by Pearson

VHDL—Packages, Sub Programs, and Sequential Circuits 16.9

2. The function body is as follows:

function get_xor4 (Signal M, N, O, P: in Std_Logic) return Std_Logic is

Signal temp: out Std_Logic; -- declare a local signal temp.

; -- declarations of logic signals M, N, O, and P are already given in the

arguments.

begin

temp: = M xor N xor O xor P; -- find the four variable XOR of M, N, O,

and P.

return temp;

end get_xor4;

3. Signal A, B, C, D: in Std_Logic_Vector;

Signal Q: out Std_Logic;

Q: = get_xor4 (A, B, C, D); -- function get_xor returning the four variable

xor into Q.

Points to Remember

1. Function does a subset of computations ...