Casio MP-2000 Service Manual page 23

[Watchdog Function]
The MP-2000 features a system protective device, watchdog timer which can generate a CPU reset when the
system comes to a halt or failure. This function is to ensure the system's reliability during unattended operation.
The trigger sources for the watchdog contain both temperature over range and system failure. The system failure
may be caused by thunder, power glitch, radio interference, software bug or whatever reason.
To activate the watchdog timer, some program code similar to the following code has to be written to the system
running loops:
:
Loop:
read (0x121)
if (END) GOTO END
GOTO Loop
END:
read (0x120)
The time-out period ranges from 0.5 to 1000 seconds. If special settings for temperature or time-out are needed,
please refer to the utility diskette.
How to Use Watchdog Function
The user can read I/O Port 121H to enable Watchdog or disable it by reading I/O Port 120H.
Reset Watchdog
Time_A
Time_B
Disable Watchdog - Read I/O Port 120H
** Time_B Time_A<Time Out
In system Run_Time, you must still have to read I/O Port 121H to reset the Watchdog timer.
If the system fails, the TSR should be stopped and Watchdog reset action will be activated.
; enable and trigger WDT
: ; interval time between triggers
; must be smaller than time-out
; period
; disable WDT
:
- Read I/O Port 121H
- Read I/O Port 121K
- Read I/O Port 121H
Setting **
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