PIC18F010 datasheet(79/176 Pages) MICROCHIP

79 / 176 page

 2001 Microchip Technology Inc.

Preliminary

DS41142A-page 77

PIC18F010/020

11.0

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.

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.

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.

Figure 11-1 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

minimum valid operating voltage specification. This

occurs at time TB. TB - TA is the total time for shut

down.

FIGURE 11-1:

TYPICAL LOW VOLTAGE DETECT APPLICATION

Time

VA = LVD trip point

VB = Minimum valid device

operating voltage

Legend:

PIC18F010 Datasheet(PDF) 79 Page - Microchip Technology