Section 11 Watchdog Timer (WDT)
Rev. 3.00 Mar. 14, 2006 Page 367 of 804
REJ09B0104-0300
Section 11 Watchdog Timer (WDT)
The watchdog timer (WDT) is an 8-bit timer that outputs an internal reset signal if a system crash
prevents the CPU from writing to the timer counter, thus allowing it to overflow.
When this watchdog function is not needed, the WDT can be used as an interval timer. In interval
timer operation, an interval timer interrupt is generated each time the counter overflows.
Figure 11.1 shows a block diagram of the WDT.
11.1 Features
•
Selectable from eight counter input clocks
•
Switchable between watchdog timer mode and interval timer mode
In watchdog timer mode
If the counter overflows, this LSI can be initialized internally.
In interval timer mode
If the counter overflows, the WDT generates an interval timer interrupt (WOVI).
Overflow
Interrupt
control
WOVI
(interrupt request
signal)
Internal reset signal
*
Reset
control
RSTCSR
TCNT
TCSR
P
φ
/2
P
φ
/64
P
φ
/128
P
φ
/512
P
φ
/2048
P
φ
/8192
P
φ
/32768
P
φ
/131072
Clock
Clock
select
Internal clocks
Bus
interface
Module bus
TCSR:
TCNT:
RSTCSR:
Note:
*
An internal reset signal can be generated by the RSTCSR setting.
Timer control/status register
Timer counter
Reset control/status register
WDT
[Legend]
Internal bus
Figure 11.1 Block Diagram of WDT
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