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M16C/6N5 Group
Reset
There are four types of resets: a hardware reset, a software reset, an watchdog timer reset, and an oscillation
stop detection reset.
Hardware Reset
A reset is applied using the RESET pin. When an "L" signal is applied to the RESET pin while the power
supply voltage is within the recommended operating condition, the pins are initialized (refer to "Table
1.5.1 Pin Status When RESET Pin Level is "L" "). The oscillation circuit is initialized and the main clock
starts oscillating. When the input level at the RESET pin is released from "L" to "H", the CPU and SFR are
initialized, and the program is executed starting from the address indicated by the reset vector. The
internal RAM is not initialized. If the RESET pin is pulled "L" while writing to the internal RAM, the internal
RAM becomes indeterminate.
Figure 1.5.1 shows the example reset circuit. Figure 1.5.2 shows the reset sequence. Table 1.5.1 shows
the statuses of the other pins while the RESET pin is "L". Figure 1.5.3 shows the CPU register status after
reset. Refer to "SFR" for SFR status after reset.
1. When the power supply is stable
(1) Apply an "L" signal to the RESET pin.
(2) Supply a clock for 20 cycles or more to the X
(3) Apply an "H" signal to the RESET pin.
2. Power on
(1) Apply an "L" signal to the RESET pin.
(2) Let the power supply voltage increase until it meets the recommended operating condition.
(3) Wait for t
d(P-R)
(4) Supply a clock for 20 cycles or more to the X
(5) Apply an "H" signal to the RESET pin.
Software Reset
When the PM03 bit in the PM0 register is set to "1" (microcomputer reset), the microcomputer has its pins,
CPU, and SFR initialized. Then the program is executed starting from the address indicated by the reset
vector.
Select the main clock for the CPU clock source, and set the PM03 bit to "1" with main clock oscillation
satisfactorily stable.
At software reset, some SFR's are not initialized. Refer to "SFR". Also, since the PM01 to PM00 bits in the
PM0 register are not initialized, the processor mode remains unchanged.
Watchdog Timer Reset
Where the PM12 bit in the PM1 register is "1" (reset when watchdog timer underflows), the microcom-
puter initializes its pins, CPU and SFR if the watchdog timer underflows. Then the program is executed
starting from the address indicated by the reset vector.
At watchdog timer reset, some SFR's are not initialized. Refer to "SFR". Also, since the PM01 to PM00
bits in the PM0 register are not initialized, the processor mode remains unchanged.
Oscillation Stop Detection Reset
Where the CM27 bit in the CM2 register is "0" (reset at oscillation stop, re-oscillation detection), the
microcomputer initializes its pins, CPU and SFR, coming to a halt if it detects main clock oscillation circuit
stop. Refer to "Oscillation Stop and Re-oscillation Detection Function".
At oscillation stop detection reset, some SFR's are not initialized. Refer to "SFR". Also, since the PM01 to
PM00 bits in the PM0 register are not initialized, the processor mode remains unchanged.
Rev.1.00
2003.05.30
page 23
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or more until the internal power supply stabilizes.
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pin.
IN
pin.
IN
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Reset
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