R8C/20 Group, R8C/21 Group 5. Resets
Rev.2.00 Aug 27, 2008 Page 24 of 458
REJ09B0250-0200
5.1 Hardware Reset
A reset is applied using the RESET pin. When an “L” signal is applied to the RESET pin while the power supply
voltage meets the recommended performance condition, the pins, CPU, and SFR are reset (refer to Table 5.2 Pin
Functions after Reset). When the input level applied to the RESET
pin changes “L” to “H”, the 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 for the CPU clock.
Refer to 4. Special Function Registers (SFRs) for the status of the SFR after reset.
The internal RAM is not reset. If the RESET
pin is pulled “L” during writing to the internal RAM, the internal
RAM will be in indeterminate state.
Figure 5.5 shows the Example of Hardware Reset Circuit and Operation and Figure 5.6 shows the 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 10µs or more.
(3) Apply “H” to the RESET
pin.
5.1.2 Power On
(1) Apply “L” to the RESET pin.
(2) Let the power supply voltage increase until it meets the recommended performance condition.
(3) Wait for td(P-R) or more to allow the internal power supply to stabilize (refer to 20. Electrical
Characteristics).
(4) Wait for 10µs or more.
(5) Apply “H” to the RESET
pin.
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