Peak 555A User’s Guide
Watch Dog Timer A-2
Port Used
Default at F2
Bit definitions of F2
D4: 1
select NMI
0
select Reset
D3: 1
Enable watch dog timer
0
Disable watch dog timer
< D2, D1, D0>: 111 :
N/A
110 :
Select 1 second
101 :
Select 2 second
100 :
Select 4 second
011 :
Select 8 second
010 :
Select 16 second
001 :
Select 32 second
000 :
Select 64 second
Watch dog Timer Programming Procedure
•
Power on or reset the system
The values of D4~D0 in port F2 are zero, i.e. the watch dog timer is disabled
•
Clear the WDT, repeatedly read port F2 with the duration no longer than the
preset
time out interval, otherwise, the WDT will generate NMI or reset the system.
