module SB_SPRAM256KA(
    input [13:0]      address,
    input [15:0]      datain,
    input [3:0]       maskwren,
    input             wren,
    input             chipselect,
    input             clock,
    input             standby,
    input             sleep,
    input             poweroff,
    output wire [15:0] dataout
);
    reg [15:0] memory [14'h3FFF:0];
    reg [15:0] output_buffer;

    integer i;

    // Default values
    wire [13:0] address_def = (address === 14'hzzzz) ? 14'h0 : address;
    wire [15:0] datain_def = (datain === 16'hzzzz) ? 16'h0 : datain;
    wire [3:0] maskwren_def = (maskwren === 4'hz) ? 4'hF : maskwren;
    wire wren_def = (wren === 1'bz) ? 1'b0 : wren;
    wire chipselect_def = (chipselect === 1'bz) ? 1'b0 : chipselect;

    wire standby_def = (standby === 1'bz) ? 1'b0 : standby;
    wire sleep_def = (sleep === 1'bz) ? 1'b0 : sleep;
    wire poweroff_def = (poweroff === 1'bz) ? 1'b0 : poweroff;

    wire [15:0] mask = {
        {8{maskwren_def[3]}},
        {8{maskwren_def[2]}},
        {8{maskwren_def[1]}},
        {8{maskwren_def[0]}}
    };

    assign dataout = (poweroff & !sleep) ? memory[address] : 16'hzzzz;

    always @(posedge clock) begin
        if (!poweroff_def) begin
            for (i = 0; i <= 14'h3FFF; i = i + 1) begin
                memory[i] = 16'hx;
            end
        end else if (!standby_def && chipselect_def && wren_def) begin
            memory[address_def] = (memory[address_def] & ~mask) | (datain & mask);
        end
    end
endmodule