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RL78/G1A CHAPTER 21 VOLTAGE DETECTOR
CHAPTER 21 VOLTAGE DETECTOR
21.1 Functions of Voltage Detector
The operation mode and detection voltages (V
LVDH, VLVDL, VLVD) for the voltage detector is set by using the option byte
(000C1H).
The voltage detector (LVD) has the following functions.
• The LVD circuit compares the supply voltage (V
DD) with the detection voltage (VLVDH, VLVDL, VLVD), and generates an
internal reset or interrupt request signal.
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• The detection level for the power supply detection voltage (V
LVDH, VLVDL, VLVD) can be selected by using the option
byte as one of 12 levels (for details, see CHAPTER 24 OPTION BYTE).
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• Operable in STOP mode.
• After power is supplied, the reset state must be retained until the operating voltage becomes in the range defined in
29.4 or 30.4 AC Characteristics. This is done by utilizing the voltage detector or controlling the externally input
reset signal. After the power supply is turned off, this LSI should be placed in the STOP mode, or placed in the
reset state by utilizing the voltage detector or controlling the externally input reset signal before the voltage falls
below the operating range. The range of operating voltage varies with the setting of the user option byte (000C2H
or 010C2H).
(a) Interrupt & reset mode (option byte LVIMDS1, LVIMDS0 = 1, 0)
The two detection voltages (V
LVDH, VLVDL) are selected by the option byte 000C1H. The high-voltage detection
level (V
LVDH) is used for releasing resets and generating interrupts. The low-voltage detection level (VLVDL) is
used for generating resets.
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(b) Reset mode (option byte LVIMDS1, LVIMDS0 = 1, 1)
The detection voltage (V
LVD) selected by the option byte 000C1H is used for generating/releasing resets.
(c) Interrupt mode (option byte LVIMDS1, LVIMDS0 = 0, 1)
The detection voltage (V
LVD) selected by the option byte 000C1H is used for releasing resets/generating interrupts.
The reset and internal interrupt signals are generated in each mode as follows.
Interrupt & Reset Mode
(LVIMDS1, LVIMDS0 = 1, 0)
Reset Mode
(LVIMDS1, LVIMDS0 = 1, 1)
Interrupt Mode
(LVIMDS1, LVIMDS0 = 0, 1)
Generates an interrupt request signal by
detecting V
DD < VLVDH when the operating
voltage falls, and an internal reset by
detecting V
DD < VLVDL.
Releases an internal reset by detecting
V
DD ≥ VLVDH.
Releases an internal reset by detecting
V
DD ≥ VLVD.
Generates an interrupt request signal by
detecting V
DD < VLVD.
Releases an internal reset by detecting
V
DD ≥ VLVD at power on after the first
release of the POR.
Generates an interrupt request signal by
detecting V
DD < VLVD or VDD ≥ VLVD at
power on after the second release of the
POR.
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While the voltage detector is operating, whether the supply voltage is more than or less than the detection level can be
checked by reading the voltage detection flag (LVIF: bit 0 of the voltage detection register (LVIM)).
Bit 0 (LVIRF) of the reset control flag register (RESF) is set to 1 if reset occurs. For details of the RESF register, see
CHAPTER 19 RESET FUNCTION.
R01UH0305EJ0200 Rev.2.00 754
Jul 04, 2013