RL78/G1H CHAPTER 22 POWER-ON-RESET CIRCUIT
R01UH0575EJ0120 Rev. 1.20 Page 755 of 920
Dec 22, 2016
CHAPTER 22 POWER-ON-RESET CIRCUIT
22.1 Functions of Power-on-reset Circuit
The power-on-reset circuit (POR) has the following functions.
• Generates internal reset signal at power on.
The reset signal is released when the supply voltage (V
DD) exceeds the detection voltage (VPOR). Note that the
reset state must be retained until the operating voltage becomes in the range defined in 31.4 AC Characteristics.
This is done by utilizing the voltage detection circuit or controlling the externally input reset signal.
• Compares supply voltage (V
DD) and detection voltage (VPDR), generates internal reset signal when VDD < VPDR.
Note that, after power is supplied, this LSI should be placed in the STOP mode, or in the reset state by utilizing the
voltage detection circuit or externally input reset signal, before the operation voltage falls below the range defined
in 31.4 AC Characteristics. When restarting the operation, make sure that the operation voltage has returned within
the range of operation.
Caution If an internal reset signal is generated in the power-on-reset circuit, the reset control flag register
(RESF) is cleared.
Remark 1. The RL78 microcontroller incorporates multiple hardware functions that generate an internal reset signal.
A flag that indicates the reset source is located in the reset control flag register (RESF) for when an
internal reset signal is generated by the watchdog timer (WDT), voltage-detector (LVD), illegal instruction
execution, RAM parity error, or illegal-memory access. The RESF register is not cleared to 00H and the
flag is set to 1 when an internal reset signal is generated by the watchdog timer (WDT), voltage-detector
(LVD), illegal instruction execution, RAM parity error, or illegal-memory access.
For details of the RESF register, see CHAPTER 21 RESET FUNCTION.
Remark 2. V
POR: POR power supply rise detection voltage
VPDR: POR power supply fall detection voltage
For details, see 31.6.2 POR characteristics.
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