Solution:

The following are relative sub-routines about watchdog timer: wdt_on() { outport(0xff76,inport(0xff76) | 0x2000); /* output mode */ outport(0xff78,inport(0xff78) & 0xdfff); /* 10 */ outport(0xff7a,inport(0xff7a) | 0x2000); /* WDI =1 */ } wdt_clear() { outport(0xff7a,inport(0xff7a) & 0xdfff); /* WDI = 0 */ outport(0xff7a,inport(0xff7a) | 0x2000); /* WDI = 1 */ } wdt_off() { outport(0xff76,inport(0xff76) & 0xdfff); /* normal mode */ outport(0xff78,inport(0xff78) & 0xdfff); /* 00 */ } From the above information, you can know where the address of watchdog timer is.