Datasheet

78K0/Kx2-L CHAPTER 22 LOW-VOLTAGE DETECTOR
R01UH0028EJ0400 Rev.4.00 671
Sep 27, 2010
CHAPTER 22 LOW-VOLTAGE DETECTOR
22.1 Functions of Low-Voltage Detector
The low-voltage detector (LVI) is mounted onto all 78K0/Kx2-L microcontroller products.
The low-voltage detector has the following functions.
• The LVI circuit compares the supply voltage (V
DD) with the LVI detection voltage (VLVI) or the input voltage from an
external input pin (EXLVI) with the LVI detection voltage (V
EXLVI = 1.21 V ±0.1 V), and generates an internal reset or
internal interrupt signal.
• The low-voltage detector (LVI) can be set to ON by an option byte by default. If it is set to ON to raise the power
supply from the POC detection voltage (V
POR = 1.61 V (TYP.)) or lower, the internal reset signal is generated when
the supply voltage (VDD) < the LVI detection voltage (VLVI = 1.91 V ±0.1 V). After that, the internal reset signal is
generated when the supply voltage (V
DD) < the LVI detection voltage (VLVI = 1.91 V ±0.1 V).
• The supply voltage (V
DD) or the input voltage from the external input pin (EXLVI) can be selected to be detected by
software.
• A reset or an interrupt can be selected to be generated after detection by software.
• Detection levels (V
LVI,16 levels) of supply voltage can be changed by software.
• Operable in STOP mode.
Remark Level detection of input voltage from external input pin (EXLVI) is available only in 78K0/KB2-L and
78K0/KC2-L.
The reset and interrupt signals are generated as follows depending on selection by software.
Selection of Level Detection of Supply Voltage (VDD)
(LVISEL = 0)
Selection Level Detection of Input Voltage from
External Input Pin (EXLVI) (LVISEL = 1)
Selects reset (LVIMD = 1). Selects interrupt (LVIMD = 0). Selects reset (LVIMD = 1). Selects interrupt (LVIMD = 0).
Generates an internal reset
signal when V
DD < VLVI and
releases the reset signal when
V
DD ≥ VLVI.
Generates an internal interrupt
signal when V
DD drops lower
than V
LVI (VDD < VLVI) or when
V
DD becomes VLVI or higher
(V
DD ≥ VLVI).
Generates an internal reset
signal when EXLVI < V
EXLVI
and releases the reset signal
when EXLVI ≥ V
EXLVI.
Generates an internal interrupt
signal when EXLVI drops
lower than V
EXLVI (EXLVI <
V
EXLVI) or when EXLVI
becomes V
EXLVI or higher
(EXLVI ≥ V
EXLVI).
Remark LVISEL: Bit 2 of low-voltage detection register (LVIM)
LVIMD: Bit 1 of LVIM
While the low-voltage detector is operating, whether the supply voltage or the input voltage from an external input pin is
more than or less than the detection level can be checked by reading the low-voltage detection flag (LVIF: bit 0 of LVIM).
When the low-voltage detector is used to reset, bit 0 (LVIRF) of the reset control flag register (RESF) is set to 1 if reset
occurs. For details of RESF, refer to CHAPTER 20 RESET FUNCTION.