Serial port on Arduino UNO

0(RX) 和 1 (TX) 這兩支腳。用來接收(RX)與傳輸(TX) TTL 訊號的序列資料。這兩支腳也連接到 USB Converter 晶片中。

不管是 UNO 還是 Nano, 它們都只有一組 UART 串列埠 TX0 與 RX0, 而且與 USB 是共接的, 亦即如果將 Arduino 的 USB 接到電腦用來上傳程式與透過 Serial.print() 來除錯與追蹤執行結果, 那麼串列埠 TX0/RX0 就不能同時接到 ESP8266 來傳送 AT 指令與接收回應.

解決之道是使用 SoftwareSerial 函式庫來將一般 DIO 針腳模擬成軟體串列埠, 參考小狐狸事務所寫的 UART 串列埠測試 :

# Arduino 串列埠測試 (UART)

但必須注意, SoftSerial not working above 19200 baud.

因此, Arduino UNO+ESP8266+SoftwareSerial 搭配使用時, Baud rate 建議使用 9600 bps.

Serial Port Options

1. HardwareSerial - Best performance. Always use this first, if available! Teensy and Teensy++ have one HardwareSerial port which is available (not used for uploading or the Arduino Serial Monitor). Arduino Mega 2560 has 3 extra HardwareSerial ports. Arduino Uno has none.
2. AltSoftSerial - Can simultaneously transmit and receive. Minimal interference with simultaneous use of HardwareSerial and other libraries. Consumes a 16 bit timer (and will not work with any libraries which need that timer) and disables some PWM pins. Can be sensitive to interrupt usage by other libraries.
3. SoftwareSerial(formerly "NewSoftSerial") - Can have multiple instances on almost any pins, but only 1 can be active at a time. Can not simultaneously transmit and receive. Can interfere with other libraries or HardwareSerial if used at slower baud rates. Can be sensitive to interrupt usage by other libraries.
4. Old SoftwareSerial (SoftwareSerial in Arduino 0023 & earlier) - Very poor performance.

SoftwareSerial Limitations

• If using multiple software serial ports, only one can receive data at a time.

• Not all pins on the Mega and Mega 2560 support change interrupts, so only the following can be used for RX: 10, 11, 12, 13, 14, 15, 50, 51, 52, 53, A8 (62), A9 (63), A10 (64), A11 (65), A12 (66), A13 (67), A14 (68), A15 (69).

• Not all pins on the Leonardo and Micro support change interrupts, so only the following can be used for RX: 8, 9, 10, 11, 14 (MISO), 15 (SCK), 16 (MOSI).

• On Arduino or Genuino 101 the current maximum RX speed is 57600bps

• On Arduino or Genuino 101 RX doesn't work on Pin 13

The library has the following known limitations:

If your project requires simultaneous data flows, see Paul Stoffregen's AltSoftSerial library. AltSoftSerial overcomes a number of other issues with the core SoftwareSerial, but has it's own limitations. Refer to the AltSoftSerial site for more information.