R8C28 datasheet(45/473 Pages) RENESAS

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R8C/28 Group, R8C/29 Group

5. Resets

Rev.2.10

Sep 26, 2008

Page 26 of 441

REJ09B0279-0210

5.1

Hardware Reset

A reset is applied using the RESET pin. When an “L” signal is applied to the RESET pin while the supply voltage

meets the recommended operating conditions, pins, CPU, and SFRs are all reset (refer to Table 5.2 Pin Functions

while RESET Pin Level is “L”). When the input level applied to the RESET pin changes from “L” to “H”, a

program is executed beginning with the address indicated by the reset vector. After reset, the low-speed on-chip

oscillator clock divided by 8 is automatically selected as the CPU clock.

Refer to 4. Special Function Registers (SFRs) for the state of the SFRs after reset.

The internal RAM is not reset. If the RESET pin is pulled “L” while writing to the internal RAM is in progress, the

contents of internal RAM will be undefined.

Figure 5.6 shows an Example of Hardware Reset Circuit and Operation and Figure 5.7 shows an Example of

Hardware Reset Circuit (Usage Example of External Supply Voltage Detection Circuit) and Operation.

5.1.1

When Power Supply is Stable

(1) Apply “L” to the RESET pin.

(2) Wait for 10

µs or more.

(3) Apply “H” to the RESET pin.

5.1.2

Power On

(1) Apply “L” to the RESET pin.

(2) Let the supply voltage increase until it meets the recommended operating conditions.

(3) Wait for td(P-R) or more to allow the internal power supply to stabilize (refer to 20. Electrical

Characteristics).

(4) Wait for 10

µs or more.

(5) Apply “H” to the RESET pin.

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