PIC18F23K20-ESLASHML datasheet(297/456 Pages) MICROCHIP

297 / 456 page

 2010 Microchip Technology Inc.

DS41303G-page 297

PIC18F2XK20/4XK20

22.5

Applications

In many applications, the ability to detect a drop below,

or rise above, a particular threshold is desirable. For

example, the HLVD module could be periodically

enabled to detect Universal Serial Bus (USB) attach or

detach. This assumes the device is powered by a lower

voltage source than the USB when detached. An attach

would indicate a high-voltage detect from, for example,

3.3V to 5V (the voltage on USB) and vice versa for a

detach. This feature could save a design a few extra

components and an attach signal (input pin).

For general battery applications, Figure 22-4 shows a

possible voltage curve. Over time, the device voltage

decreases. When the device voltage reaches voltage

VA, the HLVD logic generates an interrupt at time TA.

The interrupt could cause the execution of an ISR,

which

would

allow

the

application

perform

“housekeeping

tasks”

and

perform

controlled

shutdown before the device voltage exits the valid

operating range at TB. The HLVD, thus, would give the

application a time window, represented by the

difference between TA and TB, to safely exit.

FIGURE 22-4:

TYPICAL LOW-VOLTAGE

DETECT APPLICATION

TABLE 22-1:

REGISTERS ASSOCIATED WITH HIGH/LOW-VOLTAGE DETECT MODULE

Time

VA = HLVD trip point

VB = Minimum valid device

operating voltage

Legend:

Name

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

Reset

Values

on Page

HLVDCON

VDIRMAG

—

IRVST

HLVDEN

HLVDL3

HLVDL2

HLVDL1

HLVDL0

INTCON

GIE/GIEH PEIE/GIEL

TMR0IE

INT0IE

RBIE

TMR0IF

INT0IF

RBIF

PIR2

OSCFIF

C1IF

C2IF

EEIF

BCLIF

HLVDIF

TMR3IF

CCP2IF

PIE2

OSCFIE

C1IE

C2IE

EEIE

BCLIE

HLVDIE

TMR3IE

CCP2IE

IPR2

OSCFIP

C1IP

C2IP

EEIP

BCLIP

HLVDIP

TMR3IP

CCP2IP

Legend: — = unimplemented, read as ‘0’. Shaded cells are unused by the HLVD module.

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