PIC18F23K22-ESLASHML datasheet(345/492 Pages) MICROCHIP

345 / 492 page

 2010 Microchip Technology Inc.

Preliminary

DS41412B-page 345

PIC18(L)F2X/4XK22

23.2

HLVD Setup

To set up the HLVD module:

Select the desired HLVD trip point by writing the

value to the HLVDL<3:0> bits.

Set the VDIRMAG bit to detect high voltage

(VDIRMAG = 1) or low voltage (VDIRMAG = 0).

Enable the HLVD module by setting the

HLVDEN bit.

Clear the HLVD interrupt flag (PIR2<2>), which

may have been set from a previous interrupt.

If interrupts are desired, enable the HLVD

interrupt by setting the HLVDIE and GIE/GIEH

bits (PIE2<2> and INTCON<7>, respectively).

An interrupt will not be generated until the

IRVST bit is set.

23.3

Current Consumption

When the module is enabled, the HLVD comparator

and voltage divider are enabled and consume static

current. The total current consumption, when enabled,

is specified in Section 27.0 “Electrical Characteris-

tics”. Depending on the application, the HLVD module

does not need to operate constantly. To reduce current

requirements, the HLVD circuitry may only need to be

enabled for short periods where the voltage is checked.

After such a check, the module could be disabled.

23.4

HLVD Start-up Time

The internal reference voltage of the HLVD module,

specified

Section 27.0

“Electrical

Characteristics”, may be used by other internal

circuitry, such as the programmable Brown-out Reset.

If the HLVD or other circuits using the voltage reference

are disabled to lower the device’s current consumption,

the reference voltage circuit will require time to become

stable before a low or high-voltage condition can be

reliably detected. This start-up time, TIRVST, is an

interval that is independent of device clock speed.

The HLVD interrupt flag is not enabled until TIRVST has

expired and a stable reference voltage is reached. For

this reason, brief excursions beyond the set point may

not be detected during this interval (see Figure 23-2 or

Figure 23-3).

FIGURE 23-2:

LOW-VOLTAGE DETECT OPERATION (VDIRMAG = 0)

Note:

Before changing any module settings

(VDIRMAG, HLVDL<3:0>), first disable the

module (HLVDEN = 0), make the changes

and re-enable the module. This prevents

the generation of false HLVD events.

VHLVD

VDD

HLVDIF

VHLVD

VDD

Enable HLVD

TIRVST

HLVDIF may not be set

Enable HLVD

HLVDIF

HLVDIF cleared in software

HLVDIF cleared in software,

CASE 1:

CASE 2:

HLVDIF remains set since HLVD condition still exists

TIRVST

Internal Reference is stable

IRVST

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