Problems with ESP32 to define second UART

Hi everyone,

I am having some problems when using the second UART on the ESP32. I define this UART to use pins 14 and 33, but depending on how I define the UART I see some activity in pin 23 that is defined as an input. :o :o :o

If I configure the format: Serial1.begin(9600, SERIAL_8N1, RX_PIN, TX_PIN);
Then it seems that the TX is also present on TEST_PIN (pin 23) (checked with the oscilloscope)

If I omit the format like: Serial1.begin(9600, RX_PIN, TX_PIN);
Then there is no activity on TEST_PIN (pin 23) (checked also with the oscilloscope)

Both statements shoud be the same since SERIAL_8N1 is the default, but somehow they are not.

I do not unsderstand how these two things are related. Am I doing something wrong?. Am I missing something?. Do I have a faulty chip?.

I have not checked for other combinations. It happens that I was using pin 23 as an input for a project and this issue has driven me crazy for a copuple of days until I trace down the origin.

This is the complete code:

#include <HardwareSerial.h>

#define TX_PIN 33
#define RX_PIN 14
#define TEST_PIN 23

void setup() {
Serial.println(“Second UART test”);


Serial1.begin(9600, SERIAL_8N1, RX_PIN, TX_PIN);
// Serial1.begin(9600, RX_PIN, TX_PIN);

void loop() {

uint16_t i = 0;

for(i=0; i<10; i++){
Serial1.println(“esto es una prueba”);