PIC18C658 MICROCHIP [Microchip Technology], PIC18C658 Datasheet - Page 249

• Manufacturer Part Number: PIC18C658
• Description: High-Performance Microcontrollers with CAN Module
• Manufacturer: MICROCHIP [Microchip Technology]

21.2
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 current consumption,
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 21-3: LOW VOLTAGE DETECT WAVEFORMS
2000 Microchip Technology Inc.
Internally Generated
Reference Stable
Internally Generated
Reference Stable
CASE 1:
CASE 2:
Enable LVD
Enable LVD
Operation
LVDIF
LVDIF
V
V
DD
DD
Advanced Information
50 ms
50 ms
LVDIF may not be set
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 21-3 shows typical waveforms that the LVD
module may be used to detect.
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
PIC18CXX8
LVDIF cleared in software
V
.
V
DS30475A-page 249
LVD
LVD