SBC comm AMD SBC-770 - Manual (Page 109)

98 SBC-770 User Manual
Programming the watchdog timer
How to program the WATCHDOG TIMER
1. To set the time-out interval of watchdog timer:
-- output the desired value to port 0x443. Since the data is of 1
byte, the maximum value will be 255. In our design 2 ~ 255 will
denote 2 ~ 255 sec.
outportb(0x443, 30); // set watchdog to 30 seconds
2. To set the time-out event:
-- output data to prot 0x444,
• 0: reset system
• 1, 2, 3: IRQ 10, 15, 11 respectively
• 4: NMI
e.g.
outportb(0x444, 0); // set time-out event to reset-system
3. To disable watchdog timer:
-- output value 0 to port 0x443
outportb(0x443, 0); // disable watchdog timer
4. To ebable or refresh watchdog timer(the watchdog timer will
return to its initial value, then count down):
-- access the I/O port 0x443, e.g.
outportb(0x443, data); // refresh watchdog timer
* note: if you want to refresh the watchdog timer, you have to
disable it first.