PIC18F23K20-ESLASHML datasheet(295/456 Pages) MICROCHIP

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 2010 Microchip Technology Inc.

DS41303G-page 295

PIC18F2XK20/4XK20

22.2

HLVD Setup

The following steps are needed to set up the HLVD

module:

Write the value to the HLVDL<3:0> bits that

selects the desired HLVD trip point.

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 bit of the PIR2

previous interrupt.

Enable the HLVD interrupt if interrupts are

desired by setting the HLVDIE bit of the PIE2

CON register. An interrupt will not be generated

until the IRVST bit is set.

22.3

Current Consumption

When the module is enabled, the HLVD comparator

and voltage divider are enabled and will consume static

current. The total current consumption, when enabled,

is specified in electrical specification parameter D024B.

Depending on the application, the HLVD module does

not need to be operating constantly. To decrease the

current requirements, the HLVD circuitry may only

need to be enabled for short periods where the voltage

is checked. After doing the check, the HLVD module

may be disabled.

22.4

HLVD Start-up Time

The internal reference voltage of the HLVD module,

specified in electrical specification parameter D420,

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. It is specified in

electrical specification parameter 36.

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. Refer to Figure 22-2

or Figure 22-3.

FIGURE 22-2:

LOW-VOLTAGE DETECT OPERATION (VDIRMAG = 0)

VHLVD

VDD

HLVDIF

VHLVD

VDD

Enable HLVD

TIVRST

HLVDIF may not be set

Enable HLVD

HLVDIF

HLVDIF cleared by software

HLVDIF cleared by software,

CASE 1:

CASE 2:

HLVDIF remains set since HLVD condition still exists

TIVRST

Internal Reference is stable

IRVST

PIC18F23K20-E/ML Datasheet(PDF) 295 Page - Microchip Technology

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