ISD94100 Series Technical Reference Manual
Sep 9, 2019
Page
535
of 928
Rev1.09
IS
D
9
410
0
S
ER
IE
S
T
E
C
HN
ICA
L
RE
F
E
RE
NCE
M
AN
U
AL
1100
768
768 * 64 * T
WWDT
4.9152 s
1101
1024
1024 * 64 * T
WWDT
6.5536 s
1110
1536
1536 * 64 * T
WWDT
9.8304 s
1111
2048
2048 * 64 * T
WWDT
13.1072 s
Table 6.10.5-1 WWDT Prescaler Value Selection
6.10.5.1 WWDT Counting
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), 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.
To avoid the system is reset while CPU clock is disabled, the WWDT counter will stop counting
when CPU enters Idle/Power-down mode. After CPU enters normal mode, the WWDT counter will
start down counting.
6.10.5.2 WWDT Compare Match Interrupt
During down counting by the WWDT counter, the WWDTIF (WWDT_STATUS[0]) is set to 1 while
the WWDT counter value (CNTDAT) is equal to window compare value (CMPDAT) and WWDTIF
can be cleared by user; if INTEN (WWDT_CTL[1]) is also set to 1 by user, the WWDT compare
match interrupt signal is generated also while WWDTIF is set to 1 by hardware.
6.10.5.3 WWDT Reset System
Figure 6.10-3 shows three cases of WWDT reset and reload behavior.
Comparator
6-bit compare value
CMPDAT
6-bit down counter
value CNTDAT
from 0x3F to 0x00
Write RLDCNT
0x5AA5 will
reset system
Write RLDCNT
0x5AA5 will
reload CNTDAT
to 0x3F
CNTDAT <= CMPDAT
System reset
immediately
CNTDAT = 0
CNTDAT > CMPDAT
Figure 6.10-3 WWDT Reset and Reload Behavior