Altera code to write to address 0x0400

The following AHDL TDF file will cause the signal w400 to go high when on a write to address 0x0400, and low otherwise.
SUBDESIGN w400_eqn
    R_W             :  INPUT;
    LSTRBn          :  INPUT;
    A[15..0]        :  INPUT;  % Demultiplexed address bits % 
    w400            :  OUTPUT; % High when writing to address 0x0400 %


    if ((A[15..0] == H"0400") & (R_W == GND)) THEN
        w400 = VCC;
        w400 = GND;
    END IF;