Datasheet

CHAPTER 14 LOW-VOLTAGE DETECTOR
User’s Manual U18172EJ3V0UD
211
14.4 Operation of Low-Voltage Detector
The low-voltage detector can be used in the following two modes.
• Used as reset
Compares the supply voltage (V
DD) and detection voltage (VLVI), and generates an internal reset signal when
V
DD < VLVI, and releases internal reset when VDD ≥ VLVI.
• Used as interrupt
Compares the supply voltage (V
DD) and detection voltage (VLVI), and generates an interrupt signal (INTLVI)
when V
DD < VLVI.
The operation is set as follows.
(1) When used as reset
• When starting operation
<1> Mask the LVI interrupt (LVIMK = 1).
<2> Set the detection voltage using bits 3 to 0 (LVIS3 to LVIS0) of the low-voltage detection level select
register (LVIS).
<3> Set bit 7 (LVION) of LVIM to 1 (enables LVI operation).
<4> Use software to instigate a wait of at least 0.2 ms.
<5> Wait until “supply voltage (V
DD) ≥ detection voltage (VLVI)” at bit 0 (LVIF) of LVIM is confirmed.
<6> Set bit 1 (LVIMD) of LVIM to 1 (generates internal reset signal when supply voltage (V
DD) < detection
voltage (V
LVI)).
Figure 14-4 shows the timing of generating the internal reset signal of the low-voltage detector. Numbers <1>
to <6> in this figure correspond to <1> to <6> above.
Cautions 1. <1> must always be executed. When LVIMK = 0, an interrupt may occur immediately
after the processing in <3>.
2. If supply voltage (V
DD) ≥ detection voltage (VLVI) when LVIMD is set to 1, an internal reset
signal is not generated.
• When stopping operation
Either of the following procedures must be executed.
• When using 8-bit memory manipulation instruction: Write 00H to LVIM.
• When using 1-bit memory manipulation instruction: Clear LVIMD to 0 and LVION to 0 in that order.