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LVDI (Interrupt by Low Voltage Detect) Circuit:
Figure 14.4 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 150
µs (t
) until the reference voltage and the low-voltage-detection power supply have stabilized,
LVDON
based on overflow of LVDNT, 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 watch
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
this time, the LVDUF bit in LVDSR is set to 1 and an IRQ0 interrupt request is simultaneously
generated.
If the power supply voltage (Vcc) falls below Vreset1 (typ. = 2.3 V) voltage, the LVDR function
is performed.
Vcc
LVDINT
LVDDE
LVDDF
LVDUE
LVDUF
IRQ0 interrupt generated IRQ0 interrupt generated
Figure 14.4 Operational Timing of LVDI Circuit
Vint (U)
Vint (D)
Vreset1
VSS
Rev. 6.00, 08/04, page 433 of 628
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