R8CSLASH15 datasheet(35/277 Pages) RENESAS

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R8C/14 Group, R8C/15 Group

5. Reset

Rev.2.10

Jan 19, 2006

Page 23 of 253

REJ09B0164-0210

5.2

Power-On Reset Function

When the RESET pin is connected to the VCC pin via about 5k

Ω pull-up resistor and the VCC pin rises,

the function is enabled and the microcomputer resets its pins, CPU, and SFR. When a capacitor is

connected to the RESET pin, always keep the voltage to the RESET pin 0.8VCC or more.

When the input voltage to the VCC pin reaches to the Vdet1 level or above, count operation of the low-

speed on-chip oscillator clock starts. When the operation counts the low-speed on-chip oscillator clock

for 32 times, the internal reset signal is held “H” and the microcomputer enters the reset sequence (See

Figure 5.3). The low-speed on-chip oscillator clock divide-by-8 is automatically selected for the CPU

after reset.

Refer to 4. Special Function Register (SFR) for the status of the SFR after power-on reset.

The voltage monitor 1 reset is enabled after power-on reset.

Figure 5.6 shows the Example of Power-On Reset Circuit and Operation.

Figure 5.6

Example of Power-On Reset Circuit and Operation

NOTES:

1. Hold the voltage of the microcomputer operation voltage range (Vccmin or above) within sampling time.

2. A sampling clock can be selected. Refer to 6. Voltage Detection Circuit for details.

3. Vdet1 indicates the voltage detection level of the voltage detection 1 circuit. Refer to 6. Voltage Detection Circuit for details.

4. Refer to 19. Electrical Characteristics.

Vdet1(3)

Vpor1

Internal Reset

Signal

(“L” Valid)

tw(por1)

tw(Vpor1–Vdet1)

Sampling Time(1, 2)

Vdet1(3)

fRING-S

× 32

fRING-S

× 32

Vpor2

Vccmin

tw(por2) tw(Vpor2–Vdet1)

RESET

VCC

About

Ω

VCC

RESET

0.1V to 2.7V

0.8VCC or above

within td(P-R)

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