PIC18F258 MICROCHIP [Microchip Technology], PIC18F258 Datasheet - Page 260

• Manufacturer Part Number: PIC18F258
• Description: High Performance, 28/40-Pin Enhanced FLASH Microcontrollers with CAN
• Manufacturer: MICROCHIP [Microchip Technology]

PIC18FXX8
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 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 23-4:
DS41159B-page 258
Internally Generated
Reference Stable
Internally Generated
Reference Stable
CASE 1:
CASE 2:
Enable LVD
Enable LVD
Operation
LVDIF
LVDIF
V
V
DD
DD
LOW VOLTAGE DETECT WAVEFORMS
Preliminary
T
T
IVRST
IVRST
LVDIF may not be set
LVDIF cleared in software,
LVDIF remains set since LVD condition still exists
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.
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
LVDIF cleared in software
2002 Microchip Technology Inc.
V
.
V
LVD
LVD