illegal operation

请问piccolo系列的DSP，具体有哪些illegal operation，会进入下面的中断

interrupt void ILLEGAL_ISR(void)   // Illegal operation TRAP
{
  // Insert ISR Code here

  // Next two lines for debug only to halt the processor here
  // Remove after inserting ISR Code
  asm("          ESTOP0");
  for(;;);

}