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
). 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
µ
s (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
(4) Wait for 500
µ
s (1/fRING-S × 20).
(5) Apply “H” to the RESET pin.
