rom16_8bit.v

module rom16_8bit(
    input [3:0] addr,
    input low_o_en,
    output reg [7:0] data_out
);
    always @(addr or low_o_en)
    begin
        if(low_o_en)
        begin
            data_out = 8'bzzzzzzzz;
        end
        else
        begin

            // Change the RHS values in the assignments below to change the program that the simulation runs.
            // The computer will subtract the value at address 0x9 from the value present in address 0x8 and display the output.
            // 1 - 8 = -7
            // The instructions are: 

            // LDA 0x8
            // SUB 0x9
            // OUT
            // HLT

            // Output: 0x11111001 (-7 as 2's complement)

            case(addr)
                4'h0: data_out = 8'h08; // Program memory starts here.
                4'h1: data_out = 8'h29;
                4'h2: data_out = 8'hee;
                4'h3: data_out = 8'hff;
                4'h4: data_out = 8'h00;
                4'h5: data_out = 8'h00;
                4'h6: data_out = 8'h00;
                4'h7: data_out = 8'h00;
                4'h8: data_out = 8'h01; // Data memory starts from here.
                4'h9: data_out = 8'h08;
                4'ha: data_out = 8'h00;
                4'hb: data_out = 8'h00;
                4'hc: data_out = 8'h00;
                4'hd: data_out = 8'h00;
                4'he: data_out = 8'h00;
                4'hf: data_out = 8'h00;
            endcase
        end
    end
endmodule