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ICOP Embedded 386SX ISA Half Size AIO SBC User's Manual
2.4 Watchdog Timer
The watchdog ti m e r u s e s a 3 2 . 7 6 8 K H z f r e q u e n c y s o u r c e w i t h a 2 4 -bit
counter. Its time range stretches from 30.5 ms to 512 sec. with a resolution
of 30.5 ms. When the watchdog times out a System RESET, NMI or IRQ can
b e i n v o k e d . W a t c h d o g t i m e r c o n t r o l a n d t h e 2 4 -b i t c o u n te r i t s e l f o c c u p y 6
consecutive 8 -b i t a d d r e s s l o c a t i o n s .
When functioning properly the system resets the watchdog timer periodically
t o p r o h i b i t t h a t i t t i m e s o u t . I f t h e w a t c h d o g t i m e r t i m e s o u t , i t w i l l R E S E T
t h e s y s t e m , o r g e n e r a t e a n d N M I o r I R Q , d e p e n d i n g o n i t s c o n f i g u r a t i o n .
Watchdog or System Timer
A n o t h e r g r e a t a p p l i c a t i o n i s t o g e n e r a t e a p e r i o d i c I R Q s i g n a l . U n d e r D O S
e n v i r o n m e n t , t h e 8 2 5 4 , s y s t e m t i m e r 0 , w i l l g e n e r a t e I R Q 0 e v e r y 5 4 . 9 m s .
T h e w a t c h d o g i s l i k e s y s t e m t i m e r 0 . I t c a n b e p r o g r a m m e d to periodically
g e n e r a t e a c o n f i g u r a b l e I R Q . I t m a y b e c l e a r t h a t t h e s e l e c t e d I R Q , w i l l b e
n o l o n g e r a v a i l a b l e t o t h e s y s t e m .
Configuring the Watchdog Timer in the BIOS
The M6117D watchdog configuration register can be controlled by software
o r c a n b e s e tup in the BIOS. To do so go to BIOS Setup’s “Advanched
C h i p s e t S e t u p ”
W a t c h d o g F u n c t i o n = E n a b l e / D i s a b l e
Watchdog Signal = RESET, NMI or IRQ 3/4/5/6/7/9/10/11/12/14/15
W a t c h d o g T i m e r = 1 / 2 / 4 / 8 / 1 6 / 3 2 / 6 4 / 1 2 8 / 2 5 6 / 5 1 2 S e c o n d s
T h e B I O S s e t u p o n l y o f f e r s a l i m i te d a m o u n t o f t i m e-out values. More a
hiher resolution of timeout values refer to the next paragraph “Configuring
the Watchdog Timer by Software” Note that in case of using the BIOS setup,
t h e w a t c h d o g s t a r t s c o u n t i n g t h e m o m e n t i t p a s s e s t h e B I O S s e t u p . T h i s
m e a n s t h a t i f y o u s e t t h e t i m e-out period to 1 second, the system will keep
r e b o o t i n g b e f o r e b e i n g a b l e t o l o a d o p e r a t i n g s y s t e m o r s o f t w a r e !
A f t e r y o u h a v e f i n n i s h e d c o n f i g u r i n g y o u w a t c h d o g t i m e r r e a d “ T i m e o u t
S t a t u s & R e s e t - INDEX 3CH” on page 12 a nd look at the example on page
1 5 t o f i n d o u t h o w t o p r i o d i c a l l y r e s e t i n g t h e t i m e o u t s t a t u s t o p r e v e n t t h e
watchdog timer from invoking a RESET, NMI or IRQ.
Configuring the Watchdog Timer by Software
Chipset configuration registers