Portwell PEB-2770VG2A, Руководство пользователя

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System Installation
PEB-2770/2780VG2A User’s Manual 3-5
3.5 WDT Function
The Watchdog Timer of motherboard consists of 8-bit programmable time-out
counter and a control and status register.
WDT Controller Register
There are two PNP I/O port addresses that can be used to configure WDT.
2Eh: EFIR (Extended Function Index Register, for identifying CR index number)
2Fh: EFDR (Extended Function Data Register, for accessing desired CR)
WDT Control Mode Register
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 varies from
boards to boards.
PEB-2780 allows users to control 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 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
troubles.
The related Control Registers of WDT are all included in the following sample
program that is written in C language. User can fill a non-zero value into the
Time-out Value Register to enable/refresh WDT. System will be reset after the
Time-out Value to be counted down to zero. Or user can directly fill a zero value into
Time-out Value Register to disable WDT immediately. To ensure a successful
accessing to the content of desired Control Register, the sequence of following
program codes should be step-by-step run again when each register is accessed.
Additionally, there are maximum 2 seconds of counting tolerance that should be
considered into user’ application program. For more information about WDT, please
refer to Winbond W83627UHG data sheet.
There are two PNP I/O port addresses that can be used to configure WDT,
1) 0x2E:EFIR (Extended Function Index Register, for identifying CR index number)
2) 0x2F:EFDR (Extended Function Data Register, for accessing desired CR)