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S1C88650 TECHNICAL MANUAL EPSON 39
5 PERIPHERAL CIRCUITS AND THEIR OPERATION (Watchdog Timer)
5.3 Watchdog Timer
5.3.1 Configuration of watchdog timer
The S1C88650 is equipped with a watchdog timer
driven by OSC1 as source oscillation. The watchdog
timer must be reset periodically by software, and if
reset does not take place within the selected period,
a non-maskable interrupt signal is generated and
output to the CPU. The watchdog timer starts
operating after initial reset, however, it can be
stopped by the software.
_______
The NMI generation cycle by the watchdog timer
can be selected by mask option.
_____
Watchdog timer NMI generation cycle
■■ 32768/fOSC1
(0.75–1-sec cycle when fOSC1 = 32 kHz)
■■ 65536/fOSC1
(1.5–2-sec cycle when fOSC1 = 32 kHz)
■■ 131072/fOSC1
(3–4-sec cycle when fOSC1 = 32 kHz)
■■ 262144/fOSC1
(6–8-sec cycle when fOSC1 = 32 kHz)
Figure 5.3.1.1 is a block diagram of the watchdog
timer.
By running watchdog timer reset during the main
routine of the program, it is possible to detect
program runaway as if watchdog timer processing
had not been applied.
Normally, this routine is integrated at points that
are regularly being processed.
The watchdog timer continues to operate during
HALT and when HALT state is continuous for
longer than the selected period, the CPU starts
exception processing.
During SLEEP, the watchdog timer is stopped.
Note: The NMI generation cycles in the watchdog
timer mask option list represent maximum
values. A maximum minus (<selected
optional cycle> / 4) seconds of error occurs
depending on the watchdog timer reset
timing. For example, when 131072/fOSC1 is
selected by mask option, the actual NMI
generation cycle is within the range of
98304/fOSC1 to 131072/fOSC1 seconds.
5.3.2 Interrupt function
In cases where the watchdog timer is not periodi-
cally reset in software, the watchdog timer outputs
______
an interrupt signal to the CPU's NMI (level 4) input.
Unmaskable and taking priority over other inter-
rupts, this interrupt triggers the generation of
exception processing. See the "S1C88 Core CPU
______
Manual" for more details on NMI exception
processing.
This exception processing vector is set at 000004H.
Watchdog timer
reset signal
Watchdog timer
enable signal
Non-maskable
interrupt (NMI)
Watchdog timer
1/4
WDRST
WDEN
Divider
f
OSC1
OSC1
oscillation
circuit
1/16384
1/32768
1/65536
1/131072
Mask option
Fig. 5.3.1.1 Block diagram of watchdog timer