Peak 555A User’s Guide
Watch Dog Timer A-3
•
Initialize the SQW of RTC, set SQW output period=0.5 second
Out port 70 = 0A
Out port 71 = 2F ( generate SQW = 0.5 Sec.)
Out port 70 = 0B
Out port 71 = 0A ( enable the SQW output)
•
Select the time out intervals of WDT (decide the values of D2, D1, D0 in F2 ,
if you reset the system, i.e. D2~D0 = 0, the time out interval will be 64 sec.)
•
Select NMI or CPU reset (decide D4 value in F2 or F6, if you just reset the
system, i.e. D4 = 0, then it’s CPU reset)
•
Enable or disable WDT ( decide D3 value in F2, if you reset the
system, i.e. D3=0, it’s “disable”)
•
You should build in a mechanism in the program to always read F2 to clear
WDT before the time out of WDT.
