Example 1. Define and Use Control Registers

extern cregister volatile unsigned int IFR;
extern cregister volatile unsigned int IER;
extern int x;

main()
{
   IER = x;
   IER |= 0x100;
   printf("IER = %x\n", IER);

   IFR &= 0x100;
   IFR |= 0x100;