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

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.

98 SBC-770 User Manual