#include "mbed.h"

Serial Device(p9, p10);   // P9 and P10 UART pins

DigitalOut Led1(LED1);
DigitalOut Led2(LED2);


/**************************
** RX Interrupt Handler
**************************/
void RxInterrupt()
{
    if( Led2.read() )
    {
        Led2.write(0);
    }
    else
    {   
        Led2.write(1);
    }
}

/**************************
** Main
**************************/
int main()
{
    // Configure serial port
    Device.baud(9600);                                // Baud rate
    Device.attach( &RxInterrupt, Serial::RxIrq );     // RX interrupt handler
    
    // Initialize
    Led1.write(0);
    Led2.write(0);
    
    while(1)
    {   
        Device.putc( 0x02 );
        if( Led1.read() )
        {
            Led1.write(0);
        }
        else
        {   
            Led1.write(1);
        }
        wait( 2.0 );    // Sleep 2 second
    }
}

Hello All, I have a problem that is frustrating my progress: In order to test the USART I wrote a program to write data to the serial port on the mbed. My goal was to test the USART using a loopback and an interrupt. The idea is to send one byte out of the USART and toggle an LED in the interrupt handler when the byte is received back. When I run the program both my test LEDs remain solid. Additionally, I did not connect the TX and RX pins together so there is no reason for the LED to assert. Could you please have a look below and let me know if there is something obvious that is being overlooked? Thanks in advance!! <<code>> #include "mbed.h" Serial Device(p9, p10); // P9 and P10 UART pins DigitalOut Led1(LED1); DigitalOut Led2(LED2); /************************** ** RX Interrupt Handler **************************/ void RxInterrupt() { if( Led2.read() ) { Led2.write(0); } else { Led2.write(1); } } /************************** ** Main **************************/ int main() { // Configure serial port Device.baud(9600); // Baud rate Device.attach( &RxInterrupt, Serial::RxIrq ); // RX interrupt handler // Initialize Led1.write(0); Led2.write(0); while(1) { Device.putc( 0x02 ); if( Led1.read() ) { Led1.write(0); } else { Led1.write(1); } wait( 2.0 ); // Sleep 2 second } } <</code>>

Its called a UART. USART is a proprietary circuit that does more than just UART.