Hi.

TXD1 on ESP8266 is GPIO2 (D4).

On the ESP32:

• TXD1:GPIO 9
• RXD1: GPIO10

However, these GPIOs are internally connected to the SPI Flash of the ESP32. So, I don’t recommend using those pins.

I recommend taking a look at the following articles that describe in detail the pinout of these bords:

• ESP8266: https://randomnerdtutorials.com/esp8266-pinout-reference-gpios/
• ESP32: https://randomnerdtutorials.com/esp32-pinout-reference-gpios/

Let me know if you need further help.
Regards,
Sara

Thank you for your answer.  I need two serial ports.  If I switch to ESP32, can I use TXD2 and RXD2 instead.  I believe this is supported by the Arduino IDE.  Is there a project in the ESP32 eBook that uses the TXD2 and RXD2? 

Hi Anthonny.

If you need two serial ports in the ESP32, you can use:

• TX0 and RX0: GPIO 1 and GPIO 3
• TX2 and RX2: GPIO 17 and GPIO 16

Format for setting a serial port:

Serial.begin(baud-rate, protocol, RX pin, TX pin);

Example for initializing two serial ports:

#define RXD2 16
#define TXD2 17

#define RXD0 3
#define TXD0 1

void setup() {
Serial1.begin(9600, SERIAL_8N1, RXD2, TXD2);
Serial2.begin(9600, SERIAL_8N1, RXD0, TXD0);
}

Then, use the usual functions to interact with serial objects.

I hope this helps.
Regards,
Sara

Thank you.