R8C/1A Group, R8C/1B Group 6. Resets
Rev.1.30 Dec 08, 2006 Page 40 of 315
REJ09B0252-0130
6.1 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 6.2 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 6.4 shows an Example of Hardware Reset Circuit and Operation and Figure 6.5 shows an Example of
Hardware Reset Circuit (Usage Example of External Supply Voltage Detection Circuit) and Operation.
6.1.1 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.
6.1.2 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 19. Electrical
Characteristics).
(4) Wait for 500 µs (1/fRING-S × 20).
(5) Apply “H” to the RESET
pin.
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