Aaeon PCM-6890B, User Manual

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102 PCM-6890B User Manual
Programming the watchdog timer
Watchdog timer
The watchdog timer uses a 8-bit counter. The time range is from 32
seconds to 254.5 min with a resolution of 1 min. When timer times
out, a system reset will happen.
Configuration register
The watchdog timer of PCM-6890B is located on the chipset –
Winbond W83977. If you want to use it, you have to know how to
read/write the configuration register of W83977. The basic proce-
dure is as follows.
1. Enter configuration mode.
2. Select Logical Device.
3. Select register number.
4. Write/read data to/from register.
5. Exit configuration mode.
To Enter/Exit the configuration mode is to write a specific value to
configuration port — 3F1h.
Enter configuration mode: write value 87h to configuration port
twice.
Exit configuration mode: write value aah to configuration port.