5 RESET AND NMI
S1C33L26 TECHNICAL MANUAL
Seiko Epson Corporation
5-1
Reset and NMI
5
Initial Reset
5.1
The S1C33L26 has two initial reset sources that initialize the internal circuits.
(1) #RESET pin (external initial reset)
(2) Watchdog timer (software selectable internal initial reset)
Figure 5.1.1 shows the configuration of the initial reset circuit.
#RESET
Reset input signal
Internal reset signal
(to core and peripherals)
WDT reset signal
Watchdog
timer
Sampling circuit
1.1 Configuration of Initial Reset Circuit
Figure 5.
The CPU and peripheral circuits are initialized by the active signal from an initial reset source. When the reset sig-
nal is negated, the CPU starts reset handling. The reset handling reads the reset vector (reset handler start address)
from the beginning of the vector table and starts executing the program (initial routine) beginning with the read ad-
dress.
#RESET Pin
5.1.1
The #RESET pin is used for initial reset input from outside the IC. Set the #RESET pin to 0 (low) to reset the IC.
The #RESET input signal is sampled with the OSC3 clock. Therefore, the chip cannot be reset when the OSC3
clock is not input or generated. And as shown in Figure 5.1.1.1, to assert the internal reset signal, low level must be
continuously detected at least three times in this sampling. The #RESET signal should be held low for at least three
OSC3 clock cycles to ensure that the chip is reset. Also the internal reset signal is negated when the default OSC3
oscillation stabilization wait time has elapsed after the #RESET pin goes high.
The S1C33L26 is reset by the low state (= 0) on the internal reset signal, and starts operating when the reset signal
goes high (= 1).
OSC3 clock
#RESET
Internal
reset signal
3 cycles
Less than
3 cycles
Default OSC3 oscillation
stabilization wait time
Reset state
1.1.1 #RESET Sampling
Figure 5.
Resetting by the Watchdog Timer
5.1.2
The S1C33L26 has a built-in watchdog timer to detect runaway of the CPU. The watchdog timer outputs a signal if
it is not reset via software (due to CPU runaway) in the programmed cycles. The output signal can generate either
NMI or reset. Write 1 to the RESEN/WDT_EN register to generate reset.
For details of the watchdog timer, see the “Watchdog Timer (WDT)” chapter.
Notes: • When using the reset function of the watchdog timer, program the watchdog timer so that it
will be reset within the programmed cycles to avoid occurrence of an unnecessary reset.
• The reset function of the watchdog timer cannot be used for power-on reset as it must be en-
abled with software.