CHAPTER 23 LOW-VOLTAGE DETECTOR
User’s Manual U19780EJ2V0UD
583
23.5 Cautions for Low-Voltage Detector
In a system where the supply voltage (V
DD
) fluctuates for a certain period in the vicinity of the LVI detection voltage
(V
LVI
), the operation is as follows depending on how the low-voltage detector is used.
(1) When used as reset
The system may be repeatedly reset and released from the reset status.
In this case, the time from release of reset to the start of the operation of the microcontroller can be arbitrarily set
by taking action (1) below.
(2) When used as interrupt
Interrupt requests may be frequently generated. Take (b) of action (2) below.
<Action>
(1) When used as reset
After releasing the reset signal, wait for the supply voltage fluctuation period of each system by means of a
software counter that uses a timer, and then initialize the ports (see
Figure 23-9
).
(2) When used as interrupt
(a) Confirm that “supply voltage (V
DD
)
≥
detection voltage (V
LVI
)” when detecting the falling edge of V
DD
, or
“supply voltage (V
DD
) < detection voltage (V
LVI
)” when detecting the rising edge of V
DD
, in the servicing routine
of the LVI interrupt by using bit 0 (LVIF) of the low-voltage detection register (LVIM). Clear bit 0 (LVIIF) of
interrupt request flag register 0L (IF0L) to 0.
(b) In a system where the supply voltage fluctuation period is long in the vicinity of the LVI detection voltage, wait
for the supply voltage fluctuation period, confirm that “supply voltage (V
DD
)
≥
detection voltage (V
LVI
)” when
detecting the falling edge of V
DD
, or “supply voltage (V
DD
) < detection voltage (V
LVI
)” when detecting the rising
edge of V
DD
, using the LVIF flag, and clear the LVIIF flag to 0.
Remark
If bit 2 (LVISEL) of the low voltage detection register (LVIM) is set to “1”, the meanings of the above
words change as follows.
•
Supply voltage (V
DD
)
→
Input voltage from external input pin (EXLVI)
•
Detection voltage (V
LVI
)
→
Detection voltage (V
EXLVI
= 1.21 V)