Sony 486DX, DX4, AR-B1474 Watchdog Timer Enabled, Watchdog Timer Trigger, Watchdog Timer Disabled

AR-B1474 User¡¦s Guide

If you want to generate IRQ15 signal to warn your program when watchdog times out, the following table listed the relation of timer factors between time-out period.

Time Factor	Time-Out Period (Seconds)
0C0H	3
0C1H	6
0C2H	12
0C3H	18
0C4H	24
0C5H	30
0C6H	36
0C7H	42

Table 4-2 Time-Out Setting

NOTE: 1. If you program the watchdog to generate IRQ15 signal when it times out, you should initial IRQ15 interrupt vector and enable the second interrupt controller (8259 PIC) in order to enable CPU to process this interrupt. An interrupt service routine is required too.

2.Before you initial the interrupt vector of IRQ15 and enable the PIC, please enable the watchdog timer previously, otherwise the watchdog timer will generate an interrupt at the time watchdog timer is enabled.

4.4.2Watchdog Timer Enabled

To enable the watchdog timer, you have to output a byte of timer factor to the watchdog register whose address is Base Port+4. The following is a BASICA program which demonstrates how to enable the watchdog timer and set the time-out period at 24 seconds.

1000	REM Points to command register
1010	WD_REG% = BASE_PORT% + 4
1020	REM Timer factor = 84H (or 0C4H)
1030	TIMER_FACTOR% = %H84
1040	REM Output factor to watchdog register
1050	OUT WD_REG%, TIMER_FACTOR%
	.,etc.

4.4.3 Watchdog Timer Trigger

After you enable the watchdog timer, your program must write the same factor as enabling to the watchdog register at least once every time-out period to its previous setting. You can change the time-out period by writing another timer factor to the watchdog register at any time, and you must trigger the watchdog before the new time-out period in next trigger. Below is a BASICA program which demonstrates how to trigger the watchdog timer:

2000	REM Points to command register
2010	WD_REG% = BASE_PORT% + 4
2020	REM Timer factor = 84H (or 0C4H)
2030	TIMER_FACTOR% = &H84
2040	REM Output factor to watchdog register
2050	OUT WD_REG%, TIMER_FACTOR%
	.,etc.

4.4.4 Watchdog Timer Disabled

To disable the watchdog timer, simply write a 00H to the watchdog register.

3000	REM Points to command register
3010	WD_REG% = BASE_PORT% + 4
3020	REM Timer factor = 0
3030	TIMER_FACTOR% = 0
3040	REM Output factor to watchdog register
3050	OUT WD_REG%, TIMER_FACTOR%
	., etc.

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