
R01UH0218EJ0110 Rev.1.10
Page 99 of 664
Sep 12, 2011
R32C/142 Group and R32C/145 Group
5. Resets
5.
Resets
There are three types of operations for resetting the MCU: hardware reset, software reset, and watchdog
timer reset.
5.1
Hardware Reset
A hardware reset is generated when a low signal is applied to the
RESET pin under the recommended
operating conditions of the supply voltage. When the
RESET pin is driven low, all pins, and oscillators are
initialized (refer to Table 5.1 for details), and the main clock starts oscillating. The CPU and SFRs are
initialized by a low-to-high transition on the
RESET pin. Then, the CPU starts executing the program from
the address indicated by the reset vector. Internal RAM is not affected by a hardware reset. However, if a
hardware reset occurs during a write operation to the internal RAM, the value is undefined.
Figure 5.1 shows an example of the reset circuit.
Figure 5.2 shows the reset sequence. Table 5.1 lists pin
states while the
RESET pin is held low.
Figure 5.3 shows CPU register states after reset. Refer to 4.
“Special Function Registers (SFRs)” for details on the states of SFRs after a reset.
A. Reset when the supply voltage is stable
(1) Drive the
RESET pin low.
(2) Input at least 20 clock cycles to the XIN pin.
(3) Drive the
RESET pin high.
B. Reset when turning on the power
(1) Drive the
RESET pin low.
(2) Raise the supply voltage to the recommended operating voltage.
(3) Wait td(P-R) ms until the internal voltage is stabilized.
(4) Input at least 20 clock cycles to the XIN pin.
(5) Drive the
RESET pin high.
Figure 5.1
Reset Circuitry
VCC
RESET
0 V
VCC
0 V
RESET
Recommended
operating voltage
0.2 VCC
This width indicates internal power supply stabilization time (td(P-R))
+ at least 20 cycles of an clock input to the XIN pin