PIC18F24 MICROCHIP [Microchip Technology], PIC18F24 Datasheet - Page 264

• Manufacturer Part Number: PIC18F24
• Description: 28/40-Pin High-Performance, Enhanced Flash Microcontrollers with CAN Module
• Manufacturer: MICROCHIP [Microchip Technology]

23.2
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
constantly 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 23-4:
DS41159D-page 262
PIC18FXX8
Internally Generated
Internally Generated
Reference Stable
Reference Stable
CASE 1:
CASE 2:
Operation
Enable LVD
Enable LVD
LVDIF
LVDIF
V
V
DD
DD
LOW-VOLTAGE DETECT WAVEFORMS
T
T
IRVST
IRVST
LVDIF may not be set
The following steps are needed to set up the LVD
module:
1.
2.
3.
4.
5.
6.
Figure 23-4 shows typical waveforms that the LVD
module may be used to detect.
LVDIF cleared in software,
LVDIF remains set since LVD condition still exists
Write the value to the LVDL3:LVDL0 bits
(LVDCON 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
stabilized (clear the LVDIF bit).
Enable the LVD interrupt (set the LVDIE and the
GIE bits).
LVDIF cleared in software
 2004 Microchip Technology Inc.
LVDIF cleared in software
V
V
LVD
LVD