User’s Manual U14826EJ5V0UD
118
CHAPTER 10 WATCHDOG TIMER
10.1 Watchdog Timer Functions
The watchdog timer has the following functions:
•
Watchdog timer
•
Interval timer
Caution Select the watchdog timer mode or interval timer mode by using the watchdog timer mode
register (WDTM).
(1) Watchdog
timer
The watchdog timer is used to detect inadvertent program loops. When the inadvertent program loop is
detected, a non-maskable interrupt or a RESET signal can be generated.
Table 10-1. Inadvertent Program Loop Detection Time of Watchdog Timer
Inadvertent Program Loop
Detection Time
At f
X
= 5.0 MHz Operation
At f
CC
= 1.0 MHz Operation
2
11
×
1/f
CLK
2
11
/f
X
(410
µ
s) 2
11
/f
CC
(2.05 ms)
2
13
×
1/f
CLK
2
13
/f
X
(1.64 ms)
2
13
/f
CC
(8.19 ms)
2
15
×
1/f
CLK
2
15
/f
X
(6.55 ms)
2
15
/f
CC
(32.8 ms)
2
17
×
1/f
CLK
2
17
/f
X
(26.2 ms)
2
17
/f
CC
(131.1 ms)
Remarks 1.
f
CLK
: f
X
or f
CC
2.
f
X
:
System clock oscillation frequency (ceramic/crystal oscillation)
3.
f
CC
: System clock oscillation frequency (RC oscillation)
(2) Interval timer
The interval timer generates an interrupt at an arbitrary preset interval.
Table 10-2. Interval Time of Watchdog Timer
Interval At
f
X
= 5.0 MHz Operation
At f
CC
= 1.0 MHz Operation
2
11
×
1/f
CLK
2
11
/f
X
(410
µ
s) 2
11
/f
CC
(2.05 ms)
2
13
×
1/f
CLK
2
13
/f
X
(1.64 ms)
2
13
/f
CC
(8.19 ms)
2
15
×
1/f
CLK
2
15
/f
X
(6.55 ms)
2
15
/f
CC
(32.8 ms)
2
17
×
1/f
CLK
2
17
/f
X
(26.2 ms)
2
17
/f
CC
(131.1 ms)
Remarks 1.
f
CLK
: f
X
or f
CC
2.
f
X
:
System clock oscillation frequency (ceramic/crystal oscillation)
3.
f
CC
: System clock oscillation frequency (RC oscillation)