Kontron SBC-845D-VEA, User Manual

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SBC-845D-VEA Single Board Computer User’s Guide
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WDT Function
The working algorithm of the WDT function can be simply described as a counting process. The
Time-Out Interval can be set through software programming. The availability of the time-out
interval settings by software or hardware between boards. The SBC-845D-VEA allows users to
control the WDT through dynamic software programming. The WDT starts counting when it is
activated. It sends out a signal to system reset or to non-maskable interrupt (NMI), when the
time-out interval ends. To prevent the time-out interval from running out, a re-trigger signal will
need to be sent before the counting reaches its end. This action will restart the counting process.
A well-written WDT program should keep the counting process running under normal condition.
WDT should never generate a system reset or NMI signal unless the system runs into trouble.
The related Control Registers of WDT are all included in the following sample program that is
written in the “C” language. A user can fill a non-zero value into the Time-out Value Register to
enable/refresh the WDT. The system will be reset after the Time-out Value has counted down to
zero. Or the user can directly fill a zero value into the Time-out Value Register to disable the WDT
immediately. To successfully access the content of the desired Control Register, the sequence of
the following program codes should be run again step-by-step when each register is accessed.
Additionally, there is a maximum counting tolerance of 2 seconds that should be considered into
user’ application program. For more information about the WDT, please refer to the Winbond
W83627HF data sheet that is attached in CD accessory.
// Enter Extended Function Mode
outp(0x002E, 0x87);
outp(0x002E, 0x87);
// Assign Pin 89 to be a WDTO
outp(0x002E, 0x2B);
outp(0x002F, inp(0x002F) & 0xEF);
// Select Logic Device 8
outp(0x002E, 0x07);
outp(0x002F, 0x08);
// Active Logic Device 8
outp(0x002E, 0x30);
outp(0x002F, 0x01);