PIC18F23K20 Datasheet, PDF (289/420 Pages) Microchip Technology – 28/40/44-Pin Flash Microcontrollers with 10-Bit A/D and nanoWatt Technology

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 to perform
“housekeeping tasks” and perform a 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
VA
VB
Time ^{TA TB}
Legend: VA = HLVD trip point
VB = Minimum valid device
operating voltage
TABLE 22-1: REGISTERS ASSOCIATED WITH HIGH/LOW-VOLTAGE DETECT MODULE
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 58
INTCON GIE/GIEH PEIE/GIEL TMR0IE INT0IE RBIE TMR0IF INT0IF RBIF
57
PIR2
OSCFIF
C1IF
C2IF
EEIF
BCLIF HLVDIF TMR3IF CCP2IF
60
PIE2
OSCFIE C1IE
C2IE
EEIE BCLIE HLVDIE TMR3IE CCP2IE 60
IPR2
OSCFIP C1IP
C2IP
EEIP BCLIP HLVDIP TMR3IP CCP2IP 60
Legend: — = unimplemented, read as ‘0’. Shaded cells are unused by the HLVD module.
© 2007 Microchip Technology Inc.
Advance Information
DS41303B-page 287