R8C18 datasheet(39/257 Pages) RENESAS

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R8C/18 Group, R8C/19 Group

5. Resets

Rev.1.30

Apr 14, 2006

Page 24 of 233

REJ09B0222-0130

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 reset (refer to Table

5.2 Pin Functions after Reset). 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 5.4 shows an Example of Hardware Reset Circuit and Operation and Figure 5.5 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 500

µs (1/fRING-S × 20).

(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 condition.

(3) Wait for td(P-R) or more to allow the internal power supply to stabilize (refer to 18. Electrical

Characteristics).

(4) Wait for 500

µs (1/fRING-S × 20).

(5) Apply “H” to the RESET pin.

R8C18 Datasheet(PDF) 39 Page - Renesas Technology Corp