NUC970 Technical Reference Manual
Publication Release Date: Dec. 15, 2015
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Revision V1.30
NUC97
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The WWDT peripheral clock is enabled in WWDT (PCLKEN[1]) and clock source can be selected
in WWDT_S[1:0] (CLKDIV8[11:10]).
5.14.5 Function Description
The WWDT includes a 6-bit down counter with programmable prescale value to define different
WWDT time-out intervals. The clock source of 6-bit WWDT is based on system clock divide 4096
(PCLK/4096), external 12 MHz oscillator or internal 32 kHz oscillator with a programmable 11-bit
prescale counter value which controlled by PSCSEL (WWDT_CTL[11:8]). Also, the correlate of
PSCSEL (WWDT_CTL[11:8]) and prescale value are listed in the following table.
PSCSEL
Prescaler Value
Max. Time-Out Period
Max. Time-Out Interval
(WWDT_CLK=32 KHz)
0000
1
1 * 64 * T
WWDT
2 ms
0001
2
2 * 64 * T
WWDT
4 ms
0010
4
4 * 64 * T
WWDT
8 ms
0011
8
8 * 64 * T
WWDT
16 ms
0100
16
16 * 64 * T
WWDT
32 ms
0101
32
32 * 64 * T
WWDT
64 ms
0110
64
64 * 64 * T
WWDT
128 ms
0111
128
128 * 64 * T
WWDT
256 ms
1000
192
192 * 64 * T
WWDT
384 ms
1001
256
256 * 64 * T
WWDT
512 ms
1010
384
384 * 64 * T
WWDT
768 ms
1011
512
512 * 64 * T
WWDT
1.024 s
1100
768
768 * 64 * T
WWDT
1.536 s
1101
1024
1024 * 64 * T
WWDT
2.048 s
1110
1536
1536 * 64 * T
WWDT
3.072 s
1111
2048
2048 * 64 * T
WWDT
4.096 s
Table 5.14-1 Window Watchdog Prescaler Value Selection
WWDT Counting
5.14.5.1
When the WWDTEN (WWDT_CTL[0]) is set, WWDT down counter will start counting from 0x3F
to 0. To prevent program runs to disable WWDT counter counting unexpected, the WWDT_CTL
register can only be written once after chip is powered on or reset. User cannot disable WWDT
counter counting (WWDTEN[0]), change counter prescale period (PSCSEL) or change window
compare value (CMPDAT) while WWDTEN (WWDT_CTL[0]) has been enabled by user unless
chip is reset.