M16C29 Datasheet, PDF (59/499 Pages) Renesas Technology Corp – RENESAS MCU M16C FAMILY / M16C/Tiny SERIES

M16C/29 Group
5. Resets
5. Resets
Hardware reset 1, brown-out detection reset (hardware reset 2), software reset, watchdog timer reset, and
oscillation stop detection reset are implemented to reset the MCU.
5.1 Hardware Reset
Hardware reset 1 and brown-out detection reset are available as the hardware reset.
5.1.1 Hardware Reset 1
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Pins, CPU, and SFRs are reset by using the RESET pin. When a low-level (“L”) signal is applied to the
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RESET pin while the supply voltage meets the recommended operating condition, pins, CPU, and SFRs
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are reset (see Table 5.1 Pin Status When RESET Pin Level is “L”). The oscillation circuit is also reset and
the on-chip oscillator starts oscillating as the CPU clock. CPU and SFRs re reset when the signal applied
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to the RESET pin changes from “L” to high (“H”). The MCU executes a program beginning with the
address indicated by the reset vector. The internal RAM is not reset. When an “L” signal is applied to the
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RESET pin while writing data to the internal RAM, the content of internal RAM is undefined.
Figure 5.1 shows an example of the reset circuit. Figure 5.2 shows a reset sequence. Table 5.1 shows
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status of the other pins while the RESET pin is held “L”. Figure 5.3 shows CPU register states after reset.
Refer to 4. Special Function Register (SFR) about SFR states 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) Increase the supply voltage until it meets the the recommended performance condition
(3) Wait for td(P-R) or more to allow the internal power supply to stabilize
(4) Wait td(ROC) or more
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(5) Apply an “H” signal to the RESET pin
5.1.2 Brown-Out Detection Reset (Hardware Reset 2)
Note
Brown-out detection reset in the M16C/29 Group, T-ver. and V-ver. cannot be used.
Pins, CPU, and SFR are reset by using the on-chip voltage detection circuit, which monitors the voltage
applied to VCC pin.
When the VC26 bit in the VCR2 register is set to 1 (reset level detection circuit enabled), pins, CPU, and
SFR are reset as soon as the voltage applied to the VCC pin drops to Vdet3 or below.
Then, pins, CPU, and SFR are reset as soon as the voltage applied to the VCC pin reaches Vdet3r or
above. The MCU executes the program in an address determined by the reset vector.
The MCU executes the program after detecting Vdet3r and waiting td(S-R) ms. The same pins and
registers are reset by the hardware reset 1 and brown-out detection reset, and are also placed in the
same reset state.
The MCU cannot exit stop mode by brown-out detection reset.
Rev. 1.12 Mar.30, 2007
REJ09B0101-0112
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