
5. Reset
5.
Reset
Hardware reset, software reset, and watchdog timer reset are implemented to reset the MCU.
5.1
Hardware Reset
Pins, CPU, and SFRs are reset by using the RESET pin. When a low-level (“L”) signal is applied to the RESET pin
while the supply voltage meets the recommended performance condition, pins assigned to ports and I/O pins for
peripheral functions are reset and configured as input pins. The oscillation circuit is also reset and the main clock
starts oscillating. CPU and all the SFRs except the WDC5 bit in the WDC register are reset when the signal applied
to the RESET pin changes from “L” to high (“H”). The MCU executes a program beginning with the address
indicated by the reset vector. The internal RAM is not reset. When an “L” signal is applied to the RESET pin
while writing data to the internal RAM, the contents of the data written in internal RAM is undefined.
Figure 5.1 shows an example of the reset circuit. Figure 5.2 shows a reset sequence.
5.1.1
Reset on a Stable Supply Voltage
(1) Apply an “L” signal to the RESET pin
(2) Input 20 clock cycles or more into the XIN pin
(3) Apply an “H” signal to the RESET pin
5.1.2
Power-on Reset
(1) Apply an “L” signal to the RESET pin
(2) Increase the supply voltage until it meets the recommended performance condition
(3) Wait for td(P-R) (Internal power supply stabilization time) or more to allow the internal power supply
to stabilize
(4) Inputs 20 clock cycles or more into the XIN pin
(5) Apply an “H” signal to the RESET pin
Figure 5.1
Example of Reset Circuit
VCC
RESET
0V
VCC
0V
RESET
Recommended
operating voltage
0.2 VCC or below
Input td(P-R) + 20 clock cycles or more
to the XIN pin
0.2 VCC or below