Serial connection problem

[BluesCool]

After I use this plug-in to open the serial port com1, the message information displayed on the serial tool is incorrect. I sent aa06000000000000000000ff, but the serial tool shows 00 80 80 80 00 00 00 00 00 00 00.
Then I used the serial port tool to open com1, then closed it, and then used the plug-in to open com1, and the sent message was displayed on the serial port tool, and whatever I sent was displayed. What is the reason.

code show as below:
void open(String portName, int baudRate) async {
_serialPort = SerialPort(portName);
var config = SerialPortConfig();
config.baudRate = 9600;
config.parity = 0;
config.bits = 8;
// config.cts = 0;
// config.rts = 0;
config.stopBits = 1;
config.xonXoff = 0;
_serialPort!.config = config;
_readData();
}

void sendData(String sendData) async {
List dataList = [];
int len = sendData.length ~/ 2;
for (int i = 0; i < len; i++) {
String data = sendData.trim().substring(2 * i, 2 * (i + 1));
int? d = _hexToInt2(data);
dataList.add(d!);
}
var bytes = Uint8List.fromList(dataList);
_serialPort!.write(bytes);
}