WatchDog Timer
PRELIMINARY V1.8
29
TABLE 23.
Definition of WDCNT
10.4.
Operation
• STEP-1:
First of all, a timer interval period should be decided. Then, a WDCNT value can be
decided. Any instruction, whose destination is the WDCNT, can be used to write a value
to the WDCNT. If the content of the WDCNT is FFH, that is the initial value after any
Reset, and FFH is the needed value, you do not have to perform a write instruction to
the WDCNT.
The interval period is as follows.
WD-Timer interval time = (1 / Fselected-clock) X (WDCNT + 1) - Deviation period
0 <=Deviation period < (1 / Fselected-clock)
• STEP-2:
You should perform a write instruction to the WDCR with proper content. To turn the
WD-Timer on, you must set the WDON[1:0] to 10. While the WD-Timer is running, if
you change the content of the WDON[1:0] to 01 the WDCNT will retain its last count
value. If the WD-Timer Reset is needed, the WDREN[1:0] should be set to 10. If the
WDREN[1:0] is 01, the WD-Timer can be used as a basic interval timer. You can
choose a counting clock among four clock sources.
• STEP-3:
While the WD-Timer is running, software must repeatedly re-initialize the WDCNT
before the WD Reset is generated. This write operation can be performed without
halting the WD-Timer.
• STEP-Underflow:
BIT
7
6
5
4
3
2
1
0
NAME
WDCNT[7:0]
Definition
WatchDog Timer Register (8-bit down-counter)
Reset
Value
FFH
Read/
Write by
Software
R/W
Write by
Hardware
Written with a new count value.
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