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我正在尝试编写一个示例程序，以使用带有 apache plc4x 库的串行端口从 SHT20 温度传感器检索温度数据。

private void plcRtuReader() {

    String connectionString =
        "modbus:serial://COM5?unit-identifier=1&baudRate=19200&stopBits=" + SerialPort.ONE_STOP_BIT + "&parityBits=" + SerialPort.NO_PARITY + "&dataBits=8";

    try (PlcConnection plcConnection = new PlcDriverManager().getConnection(connectionString)) {

      if (!plcConnection.getMetadata().canRead()) {
        System.out.println("This connection doesn't support reading.");
        return;
      }

      PlcReadRequest.Builder builder = plcConnection.readRequestBuilder();
      builder.addItem("value-1", "holding-register:258[2]");
      PlcReadRequest readRequest = builder.build();

      PlcReadResponse response = readRequest.execute().get();
      for (String fieldName : response.getFieldNames()) {
        if (response.getResponseCode(fieldName) == PlcResponseCode.OK) {
          int numValues = response.getNumberOfValues(fieldName);
          // If it's just one element, output just one single line.
          if (numValues == 1) {
            System.out.println("Value[" + fieldName + "]: " + response.getObject(fieldName));
          }
          // If it's more than one element, output each in a single row.
          else {
            System.out.println("Value[" + fieldName + "]:");
            for (int i = 0; i < numValues; i++) {
              System.out.println(" - " + response.getObject(fieldName, i));
            }
          }
        }
        // Something went wrong, to output an error message instead.
        else {
          System.out.println(
              "Error[" + fieldName + "]: " + response.getResponseCode(fieldName).name());
        }
      }

      System.exit(0);
    } catch (PlcConnectionException e) {
      e.printStackTrace();
    } catch (Exception e) {
      e.printStackTrace();
    }
  }

使用串行通信与设备建立连接。但它无法获取数据，而是连续打印以下警告消息。

调试器挂在下面的行：

      PlcReadResponse response = readRequest.execute().get();

以下日志连续打印。

2021-06-03-17:41:48.425 [nioEventLoopGroup-2-1] WARN  io.netty.channel.nio.NioEventLoop - Selector.select() returned prematurely 512 times in a row; rebuilding Selector org.apache.plc4x.java.transport.serial.SerialPollingSelector@131f8986.
2021-06-03-17:41:55.080 [nioEventLoopGroup-2-1] WARN  io.netty.channel.nio.NioEventLoop - Selector.select() returned prematurely 512 times in a row; rebuilding Selector org.apache.plc4x.java.transport.serial.SerialPollingSelector@48c328c5.

使用 modpoll.exe 使用相同的 URL 数据（即波特率、stopBits 等），它可以工作并通过 RTU 返回数据。我不确定这里缺少什么。请在这里阐明一些观点。

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