PIC18F4520ESLASHMLQTP datasheet(247/390 Pages) MICROCHIP

247 / 390 page

 2004 Microchip Technology Inc.

DS39631A-page 245

PIC18F2420/2520/4420/4520

22.2

HLVD Setup

The following steps are needed to set up the HLVD

module:

Write the value to the HLVDL3:HLVDL0 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 (PIR2<2>), which

may have been set from a previous interrupt.

Enable the HLVD interrupt if interrupts are

desired by setting the HLVDIE and GIE bits

(PIE2<2> and INTCON<7>). 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 D022B.

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

detected

during

this

interval.

Refer

Figure 22-2 or Figure 22-3.

FIGURE 22-2:

LOW-VOLTAGE DETECT OPERATION (VDIRMAG = 0)

VLVD

VDD

HLVDIF

VLVD

VDD

Enable HLVD

TIVRST

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

TIVRST

Internal Reference is stable

IRVST

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