209
H'FF
H'00
H'F1
TCW count
value
H'F1 written
to TCW
Start
H'F1 written to TCW
Reset generated
TCW overflow
512 ø
osc
clock cycles
Internal reset
signal
4
×
10
6
8192
×
30
×
10
–3
= 14.6
Example: With 30 ms overflow period when ø = 4 MHz
Therefore, 256 – 15 = 241 (H'F1) is set in TCW.
Figure 9.19 Example of Watchdog Timer Operation
9.6.4
Watchdog Timer Operating Modes
Watchdog timer operating modes are shown in table 9.18.
Table 9.18
Watchdog Timer Operating Modes
Operation Mode
Reset
Active
Sleep
Watch
Sub-
active
Sub-
sleep
Standby
TCW
Reset
Functions
Functions
Halted
Halted
Halted
Halted
TCSRW
Reset
Functions
Functions
Retained
Retained
Retained
Retained