PIC18CXX2
The Low Voltage Detect circuitry is completely under
software control. This allows the circuitry to be "turned
off" by the software, which minimizes the current con-
sumption for the device.
17.0 LOW VOLTAGE DETECT
In many applications, the ability to determine if the
device voltage (VDD) is below a specified voltage level
is a desirable feature. A window of operation for the
application can be created, where the application soft-
ware can do "housekeeping tasks" before the device
voltage exits the valid operating range. This can be
done using the Low Voltage Detect module.
Figure 17-1 shows a possible application voltage curve
(typically for batteries). Over time, the device voltage
decreases. When the device voltage equals voltage VA,
the LVD logic generates an interrupt. This occurs at
time TA. The application software then has the time until
the device voltage is no longer in valid operating range
to shut down the system. Voltage point VB is the mini-
mum valid operating voltage specification. This occurs
at time TB. TB - TA is the total time for shutdown.
This module is a software programmable circuitry,
where a device voltage trip point can be specified.
When the voltage of the device becomes lower then the
specified point, an interrupt flag is set. If the interrupt is
enabled, the program execution will branch to the inter-
rupt vector address and the software can then respond
to that interrupt source.
FIGURE 17-1: TYPICAL LOW VOLTAGE DETECT APPLICATION
VA
VB
Legend:
VA = LVD trip point
VB = Minimum valid device
operating voltage
TB
TA
Time
7/99 Microchip Technology Inc.
Preliminary
DS39026B-page 175
MICROCHIP [ MICROCHIP ]
