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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.
The watchdog timer of SBC-656 is located on the chipset – Win-
bond W83977. If you want to use it, you have to know how to read/
write the configuration register of W83977. The basic procedure 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.
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SBC-656 User Manual
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