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MOPS/586 Hardware Description
Watchdog Extension
With the aid of a special Interrupt 15h function, the watchdog on a JUMPtec board can be controlled
very easily.
The respective functions have the following calling conventions:
Watchdog init
Int 15h 00h
Input:
AH = E0h
AL = 00h
BX = timeout in 0.2sec increments
CX = delay in 0.2sec increments
DX = watchdog action (0 = reset, 1 = NMI)
Output:
None
Description:
This funcion is a public JUMPtec INT15h extension used to init the
watchdog on JUMPtec boards.
Watchdog trigger
Int 15h 01h
Input:
AH = E0h
AL = 01h
Output:
None
Description:
This funcion is a public JUMPtec INT15h extension used to trigger the
watchdog on JUMPtec boards.
Detailed description of the watchdog function:
Programming:
The function Init watchdog must be called only once. The three parameters delay time, timeout time
an trigger event must be set. After initialisation the watchdog will be active only after the delay time
has expired. The watchdog must be reset during the timeout time with the trigger watchdog function.
Otherwise a RESET or NMI will occur depending on trigger event.
The trigger- and the delay time can be set in steps of 0.2 sec.
The maximum values are:
Ÿ timeout time 65535*0.2sec. = 13107s ≅ 3h 38min
Ÿ delay time 32767*0.2sec. = 6553s ≅ 1h 49min
The system BIOS makes it very easy to use the watchdog via software interrupt 15h. Two ways are
possible to access the watchdog: The simplest way is to use AH=0E0h to init or trigger the watchdog.
The second way is to use the functions ”Write I
2
C” and ”Read I
2
C” with AH=0E1h and handling the I
2
C
bus protocol.
A) Simple with AH = E0h
Init Watchdog (Int 15h, AH=E0h)
Called with AX E000h
BX timeout time
BX = 0 ð watchdog off. BX
max
= 0FFFFh
CX delay time
CX = 0 ð no delay. CX
max
= 07FFFh
DX trigger event
DX = 0 ð RESET, DX = 1 ð IOCHCHK
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