M16C26A Datasheet, PDF (43/352 Pages) Renesas Technology Corp – 16-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M16C/Tiny SERIES

M16C/26A Group (M16C/26A, M16C/26B, M16C/26T)
5. Reset
5. Reset
There are four types of resets: a hardware reset, a software reset, an watchdog timer reset, and an oscilla-
tion stop detection reset.
5.1 Hardware Reset
There are two types of hardware resets: a hardware reset 1 and a hardware reset 2.
5.1.1 Hardware Reset 1
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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 (see
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Table 5.1.1.1 Pin Status When RESET Pin Level is “L”). The internal on-chip oscillator is initialized
and used as CPU clock.
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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
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is not initialized. If the RESET pin is pulled “L” while writing to the internal RAM, the internal RAM
becomes indeterminate.
Figure 5.1.1.1 shows the example reset circuit. Figure 5.1.1.2 shows the reset sequence. Table
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5.1.1.1 shows the status of the other pins while the RESET pin is “L”. Figure 5.1.1.3 shows the CPU
register status after reset. Refer to “SFR Map” for SFR status after reset.
1. When the power supply is stable
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(1) Apply an “L” signal to the RESET pin.
(2) Wait td(ROC) or more.
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(3) Apply an “H” signal to the RESET pin.
2. Power on
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(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 td(P-R) or more until the internal power supply stabilizes.
(4) Wait td(ROC) or more.
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(5) Apply an “H” signal to the RESET pin.
5.1.2 Hardware Reset 2
Note
M16C/26T does not use this function.
This reset is generated by the microcomputer’s internal voltage detection circuit. The voltage detec-
tion circuit monitors the voltage supplied to the VCC pin.
If the VC26 bit in the VCR2 register is set to “1” (reset level detection circuit enabled), the microcom-
puter is reset when the voltage at the VCC input pin drops below Vdet3.
Conversely, when the input voltage at the VCC pin rises to Vdet3r or more, the pins and the CPU and
SFR are initialized, and the program is executed starting from the address indicated by the reset
vector. It takes about td(S-R) before the program starts running after Vdet3r is detected. The initialized
pins and registers and the status thereof are the same as in hardware reset 1.
The microcomputer cannot exit stop mode by voltage down detection reset (hardware reset 2).
Rev. 2.00 Feb.15, 2007 ^{page 26} of 329
REJ09B0202-0200