In general, when an interrupt occurs in the code, the microcontroller immediately stops executing the code it runs, and starts executing an interrupt routine instead. It is important that the environment of the interrupted function is restored after the interrupt is handled—this includes the values of processor registers and the processor status register. This makes it possible to continue the execution of the original code after the code that handled the interrupt was executed.

the RL78 microcontroller supports many interrupt sources. For each interrupt source, an interrupt routine can be written. Each interrupt routine is associated with a vector number, which is specified in the documentation from the chip manufacturer. If you want to handle several different interrupts using the same interrupt routine, you can specify several interrupt vectors.

For the RL78microcontroller, the interrupt vector table always starts at the address 0x0 and is placed in the .intvec section. The interrupt vector is the offset into the interrupt vector table.

By default, the vector table is populated with a default interrupt handler which calls the abort function. For each interrupt source that has no explicit interrupt service routine, the default interrupt handler will be called. If you write your own service routine for a specific vector, that routine will override the default interrupt handler.

The header file iodevice.h, where device corresponds to the selected device, contains predefined names for the existing interrupt vectors.

To define an interrupt function, the __interrupt keyword and the #pragma vector directive can be used. For example:

#pragma vector = INTP2_vect /* Symbol defined in I/O header file */
__interrupt void MyInterruptRoutine(void)
{
  /* Do something */
}