HD64F3694FXV Datasheet, PDF (325/452 Pages) Renesas Technology Corp – Old Company Name in Catalogs and Other Documents

Section 18 Power-On Reset and Low-Voltage Detection Circuits (Optional)
VCC
VLVDRmin
LVDRES
Vreset
VSS
PSS-reset
signal
OVF
Internal reset
signal
131,072 cycles
PSS counter starts
Reset released
Figure 18.3 Operational Timing of LVDR Circuit
LVDI (Interrupt by Low Voltage Detect) Circuit:
Figure 18.4 shows the timing of LVDI functions. The LVDI enters the module-standby state after
a power-on reset is canceled. To operate the LVDI, set the LVDE bit in LVDCR to 1, wait for 50
µs (t_LVDON) until the reference voltage and the low-voltage-detection power supply have stabilized
by a software timer, etc., then set the LVDDE and LVDUE bits in LVDCR to 1. After that, the
output settings of ports must be made. To cancel the low-voltage detection circuit, first the
LVDDE and LVDUE bits should all be cleared to 0 and then the LVDE bit should be cleared to 0.
The LVDE bit must not be cleared to 0 at the same timing as the LVDDE and LVDUE bits
because incorrect operation may occur.
When the power-supply voltage falls below Vint (D) (typ. = 3.7 V) voltage, the LVDI clears the
LVDINT signal to 0 and the LVDDF bit in LVDSR is set to 1. If the LVDDE bit is 1 at this time,
an IRQ0 interrupt request is simultaneously generated. In this case, the necessary data must be
saved in the external EEPROM, etc, and a transition must be made to standby mode or subsleep
mode. Until this processing is completed, the power supply voltage must be higher than the lower
limit of the guaranteed operating voltage.
When the power-supply voltage does not fall below Vreset1 (typ. = 2.3 V) voltage but rises above
Vint (U) (typ. = 4.0 V) voltage, the LVDI sets the LVDINT signal to 1. If the LVDUE bit is 1 at
Rev.5.00 Nov. 02, 2005 Page 295 of 418
REJ09B0028-0500