Gurux.DLMS.GXDLMS.GetHdlcFrame C# (CSharp) Method

        internal static byte[] GetHdlcFrame(GXDLMSSettings settings, byte frame, GXByteBuffer data)
        {
            GXByteBuffer bb = new GXByteBuffer();
            int frameSize, len = 0;
            byte[] primaryAddress, secondaryAddress;
            if (settings.IsServer)
            {
                primaryAddress = GetHdlcAddressBytes(settings.ClientAddress, 0);
                secondaryAddress = GetHdlcAddressBytes(settings.ServerAddress, settings.ServerAddressSize);
            }
            else
            {
                primaryAddress = GetHdlcAddressBytes(settings.ServerAddress, settings.ServerAddressSize);
                secondaryAddress = GetHdlcAddressBytes(settings.ClientAddress, 0);
            }
            // Add BOP
            bb.SetUInt8(GXCommon.HDLCFrameStartEnd);
            frameSize = Convert.ToInt32(settings.Limits.MaxInfoTX);
            // If no data
            if (data == null || data.Size == 0)
            {
                bb.SetUInt8(0xA0);
            }
            else if (data.Size - data.Position <= frameSize)
            {
                // Is last packet.
                bb.SetUInt8(0xA0);
                len = data.Size - data.Position;
            }
            else
            {
                // More data to left.
                bb.SetUInt8(0xA8);
                len = frameSize;
            }
            //Frame len.
            if (len == 0)
            {
                bb.SetUInt8((byte)(5 + primaryAddress.Length + secondaryAddress.Length + len));
            }
            else
            {
                bb.SetUInt8((byte)(7 + primaryAddress.Length + secondaryAddress.Length + len));
            }
            // Add primary address.
            bb.Set(primaryAddress);
            // Add secondary address.
            bb.Set(secondaryAddress);

            //Add frame ID.
            if (frame == 0)
            {
                frame = settings.NextSend();
            }
            bb.SetUInt8(frame);
            // Add header CRC.
            UInt16 crc = GXFCS16.CountFCS16(bb.Data, 1, bb.Size - 1);
            bb.SetUInt16(crc);
            if (len != 0)
            {
                //Add data.
                bb.Set(data, len);
                // Add data CRC.
                crc = GXFCS16.CountFCS16(bb.Data, 1, bb.Size - 1);
                bb.SetUInt16(crc);
            }
            // Add EOP
            bb.SetUInt8(GXCommon.HDLCFrameStartEnd);
            if (data != null)
            {
                //Remove sent data in server side.
                if (settings.IsServer)
                {
                    if (data.Size == data.Position)
                    {
                        data.Clear();
                    }
                    else
                    {
                        data.Move(data.Position, 0, data.Size - data.Position);
                        data.Position = 0;
                    }
                }
            }
            return bb.Array();
        }