I-Bus Hawkfish, User Manual

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Hawkfish User’s Guide
A1-3
Watch Dog Timer Programming Procedure
Power on or reset the system
The initial value of WDT Control Register (D4~D0) is zero, when the
power is on or when the system is reset. The following means the initial
value of WDT (00000000b):
Bit Value Mean
4 0 Select Reset
3 0 Disable watch dog timer
2, 1, 0 0 0 0 Select 64 second
Initialize the SQW of RTC (set SQW output period=0.5 second)
To initialize the SQW of the RTC processor is to set the SQW signal
whose output period=0.5 second. It offers the basic frequency of the
WDT counter.
The following is an example of initializing the SQW signal program in
Intel 8086 assembly language.
; (Generate SQW = 0.5 Sec.)
Mov dx, 70h
Mov ax, 0Ah
Out dx, al ; Out port 70h = 0Ah
Mov dx, 71h
Mov ax, 2Fh
Out dx, al ; Out port 71h = 2Fh
; (enable the SQW output)
Mov dx, 70h
Mov ax, 0Bh
Out dx, al ; Out port 70h = 0Bh
Mov dx, 71h
Mov ax, 0Ah
Out dx, al ; Out port 71h = 0Ah
Appendix 1 - Watch Dog Timer