Technical Manual "Thunderbird/MM” Version 1.2
12.08.2005
Page 16 of 48
1.25 Watchdog
The watchdog timer consists of an 8-bit counter and three registers: Timeout register (WDTO), Mask
register (WDMSK) and Status register (WDST). The counter is an 8-bit down counter that is clocked
every minute or second and is used for the timeout period countdown. The WDTO register holds the
programmable timeout, which is the period of inactivity after which the watchdog timer prompts the
system (1 to 255 minutes or seconds). The WDMSK register determines which system events are
enabled as watchdog Timer trigger events to restart the countdown. The WDST register holds the
watchdog timer status bit that reflects the value of the WDO pin and indicates that the timeout period
has expired. In addition, it sets the time unit (minutes or seconds). The figure shows the functionality
of the watchdog timer.
Please check the Super-I/O's datasheet for details about the operation and the signals.
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