gistfile1.cs

public static Task<byte[]> WaitData(this SerialPort serialPort, TimeSpan timeout, byte[] request)
{
    var tcs = new TaskCompletionSource<byte[]>();

    SerialDataReceivedEventHandler handler = null;
    Timer timer = null;

    handler = (sender, e) =>
    {
        var package = serialPort.ReadPackage();
        if (package.SequenceEqual(request) == false)
        {
            tcs.TrySetResult(package);
            serialPort.DataReceived -= handler;
            timer.Dispose();
        }
    };

    timer = new Timer(sender =>
    {
        tcs.TrySetResult(null);
        serialPort.DataReceived -= handler;
        timer.Dispose();
    }, null, (int)timeout.TotalMilliseconds, Timeout.Infinite);

    serialPort.DataReceived += handler;

    return tcs.Task;
}