Impact-E 3x series embedded computer user manual
Page 37 of 40
B. Appendix B: Watchdog Timer
B.1 Introduction
A watchdog timer is a piece of hardware that can be used to automatically detect system anomalies and reset
the processor in the case any problems are found. Generally speaking, a watchdog timer is based on a
counter that counts down from an initial value to zero. The software selects the counter's initial value and
periodically restarts it. Should the counter reach zero before the software restarts it, the software is presumed
to be malfunctioning, and the processor's reset signal is asserted. Thus, the processor will be restarted as if a
human operator had cycled the power.
B.2 Register Descriptions
A watchdog action consists of a series of watchdog instructions. The watchdog function is controlled by a
number of register values. This section describes the detail register in LPD I/O (W83697UHG).
B.2.1 Watchdog timer usage
For DOS system:
Execute the WD.EXE file under DOS (WD.EXE and CWSDPMI.EXE should be placed on same directory),
then key-in 0~255. The system will reboot automatically according to the time-out you set.
NOTE:
The watchdog function is from the WINBOND 83627UHG.
Examples can be found on the Amplicon CD in the watchdog
folder.
Watchdog Timer is controlled by CRF5, CRF6, CRF7 of Logical Device.
CRF5 (PLED mode register. Default 0x00)
Bit 7-6 : select PLED mode
= 00 Power LED pin is tri-stated.
= 01 Power LED pin is drived low.
= 10 Power LED pin is a 1Hz toggle pulse with 50 duty cycle
= 11 Power LED pin is a 1/4Hz toggle pulse with 50 duty cycle.
Bit 5-4 : Reserved
Bit 3 : select WDTO count mode.
= 0 second
= 1 minute
Bit 2 : Enable the rising edge of keyboard Reset(P20) to force Time-out event.
= 0 Disable
= 1 Enable
Bit 1-0 : Reserved
CRF6 (Default 0x00) - Watchdog Timer Time-out value
Writing a non-zero value to this register will load the watchdog counter and start counting down. If the Bit 7
and Bit 6 are set, any mouse Interrupt or keyboard interrupt event will reload the previously-loaded non-zero
value. Reading this register will return the current value in the watchdog counter and not the watchdog timer
time-out value.
Bit 7 - 0 = 0x00 Time-out Disable
= 0x01 Time-out occurs after 1 second/minute
= 0x02 Time-out occurs after 2 second/minutes
= 0x03 Time-out occurs after 3 second/minutes
= 0xFF Time-out occurs after 255 second/minutes
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