A powerful construct for specifying combinational logic is when/else:

OUTPUT <= VALUE when (CONDITION) else OTHER_VALUE;


Complete the architecture below to build a 8-bit 2:1 multiplexer. The inputs A and B are each 8 bits, and select line S is a single bit. When S is low, all 8 bits of A should be connected to the output Y; when S is high, the 8 bits of B should go to the output.

library IEEE; use IEEE.std_logic_1164.all; entity mux21 is port( a : in std_logic_vector(7 downto 0); b : in std_logic_vector(7 downto 0); s : in std_logic; y : out std_logic_vector(7 downto 0) ); end mux21; architecture synth of mux21 is begin y <= x"00"; -- Replace this end;