entity SMODEL is
  port 
    (P1 : in BIT;
     P2 : out BIT;
     P3 : inout BIT);
end SMODEL;

architecture STRUCTURE of SMODEL is
  component UNIT
    port (C1, C2 : in BIT;
          C3 : out BIT);
  end component;
begin
  U1 : UNIT port map (C1 => P1, C2 => P3, C3=> P2);
end STRUCTURE;

architecture STRUCTURE_A of SMODEL is
  component UNIT
    port (C1, C2 : in BIT;
          C3 : out BIT);
  end component;
begin
  U2 : UNIT port map (C1 => P3, C2 => P1, C3=> P2);
end STRUCTURE_A;