PIC18C242 MICROCHIP [Microchip Technology], PIC18C242 Datasheet - Page 178

• Manufacturer Part Number: PIC18C242
• Description: High-Performance Microcontrollers with 10-Bit A/D
• Manufacturer: MICROCHIP [Microchip Technology]

PIC18CXX2
17.2
Depending on the power source for the device voltage,
the voltage normally decreases relatively slowly. This
means that the LVD module does not need to be con-
stantly operating. To decrease the current require-
ments, the LVD circuitry only needs to be enabled for
short periods, where the voltage is checked. After
doing the check, the LVD module may be disabled.
Each time that the LVD module is enabled, the circuitry
requires some time to stabilize. After the circuitry has
stabilized, all status flags may be cleared. The module
will then indicate the proper state of the system.
FIGURE 17-3: LOW VOLTAGE DETECT WAVEFORMS
DS39026B-page 178
Internally Generated
Reference stable
Internally Generated
Reference stable
CASE 1:
CASE 2:
Enable LVD
Enable LVD
Operation
LVDIF
LVDIF
V
V
DD
DD
50 ms
50 ms
LVDIF may not be set
Preliminary
LVDIF cleared in software,
LVDIF remains set since LVD condition still exists
The following steps are needed to setup the LVD
module:
1.
2.
3.
4.
5.
6.
Figure 17-3 shows typical waveforms that the LVD
module may be used to detect.
Write the value to the LVDL3:LVDL0 bits (LVD-
CON register), which selects the desired LVD
Trip Point.
Ensure that LVD interrupts are disabled (the
LVDIE bit is cleared or the GIE bit is cleared).
Enable the LVD module (Set the LVDEN bit in
the LVDCON register).
Wait for the LVD module to stabilize (the IRVST
bit to become set).
Clear the LVD interrupt flag, which may have
falsely become set until the LVD module has sta-
bilized (clear the LVDIF bit).
Enable the LVD interrupt (set the LVDIE and the
GIE bits).
LVDIF cleared in software
LVDIF cleared in software
7/99 Microchip Technology Inc.
V
.
V
LVD
LVD