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The USART_UDRE_vect is an interrupt handler that is called when a data can be transmitted using serial communication. This routine calls HardwareSerial::_tx_udr_empty_irq().

Source Code

The USART_UDRE_vect is defined in hardware/arduino/avr/cores/arduino/HardwareSerial0.cpp as below.

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 ISR(USART_RX_vect)
{
    Serial._tx_udr_empty_irq();
}

The ISR() a macro to define an interrupt handler.

This function calls HardwareSerial::_tx_udr_empty_irq().

Version

Arduino AVR Boards 1.8.6

Last Update

March 21, 2023