R8C2K datasheet(44/471 Pages) RENESAS

44 / 471 page

R8C/2K Group, R8C/2L Group

5. Resets

Rev.1.10

Dec 21, 2007

Page 27 of 450

REJ09B0406-0110

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 5.5 shows an Example of Hardware Reset Circuit and Operation and Figure 5.6 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.

(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 22. Electrical

Characteristics).

(4) Wait for 10

µs.

(5) Apply “H” to the RESET pin.

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