Rev. 1.0, 09/02, page 283 of 568
Section 13 Watchdog Timer
The watchdog timer (WDT) is an 8-bit timer that can generate an internal reset signal for this LSI
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.
The block diagram of the WDT is shown in figure 13.1.
13.1 Features
•
Selectable from eight counter input clocks.
•
Switchable between watchdog timer mode and interval timer mode
In watchdog timer mode
•
If the counter overflows, it is possible to select whether this LSI is internally reset or not.
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
TSCR
φ
/2
φ
/64
φ
/128
φ
/512
φ
/2048
φ
/8192
φ
/32768
φ
/131072
Clock
Clock
select
Internal clock
sources
Bus
interface
Module bus
TCSR
TCNT
RSTCSR
Note:
*
The type of internal reset signal depends on a register setting.
: Timer control/status register
: Timer counter
: Reset control/status register
WDT
Legend
Internal bus
Figure 13.1 Block Diagram of WDT
WDT0100A_000020020300
Summary of Contents for H8S/2627
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