
User’s Manual U19780EJ2V0UD
552
CHAPTER 21 RESET FUNCTION
The reset function
is mounted onto all 78K0/Kx2-A microcontroller products.
The following four operations are available to generate a reset signal.
(1) External reset input via RESET pin
(2) Internal reset by watchdog timer program loop detection
(3) Internal reset by comparison of supply voltage and detection voltage of power-on-clear (POC) circuit
(4) Internal reset by comparison of supply voltage and detection voltage of low-power-supply detector (LVI)
External and internal resets have no functional differences. In both cases, program execution starts at the address
at 0000H and 0001H when the reset signal is generated.
A reset is applied when a low level is input to the RESET pin, the watchdog timer overflows, or by POC and LVI
circuit voltage detection, and each item of hardware is set to the status shown in Tables 21-1 and 21-2. Each pin is
high impedance during reset signal generation or during the oscillation stabilization time just after a reset release.
When a low level is input to the RESET pin, the device is reset. It is released from the reset status when a high
level is input to the RESET pin and program execution is started with the internal high-speed oscillation clock after
reset processing. A reset by the watchdog timer is automatically released, and program execution starts using the
internal high-speed oscillation clock (see
Figures 21-2
to
21-4
) after reset processing. Reset by POC and LVI circuit
power supply detection is automatically released when V
DD
≥
V
POC
or V
DD
≥
V
LVI
after the reset, and program
execution starts using the internal high-speed oscillation clock (see
CHAPTER 22 POWER-ON-CLEAR CIRCUIT
and
CHAPTER 23 LOW-VOLTAGE DETECTOR
) after reset processing.
Cautions 1. For an external reset, input a low level for 10
μ
s or more to the RESET pin.
2. During reset signal generation, the X1 clock, XT1 clock
Note
, internal high-speed oscillation
clock, and internal low-speed oscillation clock stop oscillating. External main system clock
input become invalid.
3. When the STOP mode is released by a reset, the STOP mode contents are held during reset
input. However, the port pins become high-impedance.
Note
The 78K0/KB2-A is not provided with XT1 clock.