To use the hardware serial on the M5Stack, you can simply use the standard Serial library in your Arduino code instead of the SoftwareSerial library. The hardware serial on the M5Stack is available on pins 1 (TX) and 3 (RX) of the Grove connector, so you need to connect the RFID module's TX pin to the M5Stack's RX pin and vice versa.

Here's an example code to get you started with using the hardware serial on the M5Stack:
#include <M5Stack.h>

void setup() {
M5.begin();
Serial.begin(9600);
}

void loop() {
if (Serial.available() > 0) {
// read data from serial and process it
// ...
}
}

In this example, we initialize the M5Stack library and then start the hardware serial communication with a baud rate of 9600. In the loop() function, we check if there is any data available on the serial port, and if there is, we can read it and process it accordingly.

I hope this helps! Let me know if you have any more questions.

I'm also trying to make the same RFID reader work with my ExtPort by using the port C and UART

But I cannot get any value from the reader.
Can somebody help me in this ?

Here are the details of my setup.

Thank you very much
Regards

On M5Stack (Fire, Gray, Basic) the red Groove port A is only usable for I2C communication. The reason is that the same GPIOs (21, 22) are used internally for I2C communication with the IP5306 and therefore cannot be reprogrammed to be used as serial port.

Please also check out Pin Map for red Groove Port A here.

For serial communication you'd need a M5GO Bottom (or Bottom2) which provides you with the blue Groove port C.

Thanks
Felix