M16C28 Datasheet, PDF (52/423 Pages) Renesas Technology Corp – 16-BIT SINGLE-CHIP MICROCOMPUTER M16C FAMILY / M16C/Tiny SERIES

M16C/28 Group (M16C/28, M16C/28B)
5. Reset
5. Reset
Hardware reset, software reset, watchdog timer reset and oscillation stop detection reset are available to
initialize the microcomputer.
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 supply
voltage is within the recommended operating condition, the pins are initialized (see Table 5.1 Pin Status
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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 is not
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initialized. If the RESET pin is pulled “L” while writing to the internal RAM, the internal RAM becomes
indeterminate.
Figure 5.1 shows the example reset circuit. Figure 5.2 shows the reset sequence. Table 5.1 shows the
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status of the other pins while the RESET pin is held “L”. Figure 5.3 shows the CPU register status after
reset. Refer to 4. Special Function Register (SFR) for SFR status after reset.
1. Reset on a stable supply voltage
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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 reset
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(1) Apply an “L” signal to the RESET pin.
(2) Raise the supply voltage to the recommended operating level.
(3) Insert td(P-R) as wait time for the internal voltage is stabilized.
(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
This reset is generated by the microcomputer’s internal voltage detection circuit. The voltage detection
circuit monitors the voltage applied to the VCC pin.
If the VC26 bit in the VCR2 register is set to “1” (reset level detection circuit enabled), the microcomputer
is reset when the voltage at the VCC input pin drops Vdet3 or below.
Conversely, when the input voltage at the VCC pin rises to Vdet3 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 Vdet3 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 brown-out detection reset (hardware reset 2).
Rev. 2.00 Jan. 31, 2007 ^{page 32} of 385
REJ09B0047-0200