System Installation
PEB-2737VLA User
’s Manual
3-4
3.5
WDT Function
The algorithm of the WDT function can be simply described as a timer counting
process with an output event. The Time-Out period ( T
wd
) can be set by software
commands or hardware jumpers that depend on the board circuit design and may be
different among the boards. This timer can be used to monitor a software hang.
PEB-2737VLA allows users to control WDT by issuing dynamic software commands.
The WDT starts counting when it is activated. It will cause a system reset once it
expires. Before WDT expires, a refreshing command with a T
wd
can be issued to re-
count WDT and continue the status monitoring. If the system encounters a software
or application hang, WDT will generate a system reset after its timeout.
The related Control Registers of WDT are included in the following programming
guide that is written in C language. User can write a non-zero value ( defined as
T
wd
) into the Time-out Value Register ( CR_T
wd
) to enable WDT. Users can write
0x00 and then T
wd
to CR_T
wd
to refresh WDT. To refresh WDT, the time tolerance of
refreshing interval must be considered. The smaller of T
wd
, the more deviation of
WDT and you need to include more tolerance. “Let T
wd
be longer than 2 seconds” is
the recommendation due to the limitation of Winbond W83627DHG WDT. You can
call Portwell support center for reference. The value read back from CR_T
wd
indicates the counting down value instead of the original T
wd
. System will be reset
after the Time-out Value to be counted down to zero. Users can directly fill a zero
value into CR_T
wd
to disable WDT immediately. To ensure a successful access to the
desired Control Register, the following programming guide should be followed.
Programming guide :
CR : Configuration Register.
LD : Logical Device of SIO . There are 11 LDs in W83627DHG SIO.
CR00~2F : Global Control Registers. ( All LDs share these CRs )
CR07 : LD selection.
CR30~FF : Each LD has its own CR30~FF.
