public class RS232 : MonoBehaviour {
    private const int HEADER_LENGTH = 7;

    private const byte header = 0xA6;

    private byte[] BuildPacket (int monitorID, params byte[] data) {
        byte[] packet = new byte[HEADER_LENGTH + data.Length + 1];

        packet[0] = header; // header
        packet[1] = (byte)monitorID; // monitor ID
        packet[2] = 0; // category (fixed)
        packet[3] = 0; // code0 (fixed)
        packet[4] = 0; // code1
        packet[5] = (byte) (data.Length + 3); // length
        packet[6] = 1; // data control (fixed)

        // data
        for (int i = 0; i < data.Length; i++) {
            packet[HEADER_LENGTH + i] = data[i];
        }

        // checksum
        byte checkSum = 0;
        for (int i = 0; i < packet.Length - 1; i++) {
            checkSum ^= packet[i];
        }
        packet[packet.Length - 1] = checkSum;

        return packet;
    }
}