PIC16F737-I/SP【PDF 145/231 页】IC PIC MCU FLASH 4KX14 28DIP

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PIC18F2X1X/4X1X

DS39636D-page 234

2009 Microchip Technology Inc.

The module is enabled by setting the HLVDEN bit.

Each time that the HLVD module is enabled, the

circuitry requires some time to stabilize. The IRVST bit

is a read-only bit and is used to indicate when the circuit

is stable. The module can only generate an interrupt

after the circuit is stable and IRVST is set.

The VDIRMAG bit determines the overall operation of

the module. When VDIRMAG is cleared, the module

monitors for drops in VDD below a predetermined set

point. When the bit is set, the module monitors for rises

in VDD above the set point.

21.1

Operation

When the HLVD module is enabled, a comparator uses

an internally generated reference voltage as the set

point. The set point is compared with the trip point,

where each node in the resistor divider represents a

trip point voltage. The “trip point” voltage is the voltage

level at which the device detects a high or low-voltage

event, depending on the configuration of the module.

When the supply voltage is equal to the trip point, the

voltage tapped off of the resistor array is equal to the

internal reference voltage generated by the voltage

reference module. The comparator then generates an

interrupt signal by setting the HLVDIF bit.

The trip point voltage is software programmable to any

one of 16 values. The trip point is selected by

programming

the

HLVDL3:HLVDL0

bits

(HLVDCON<3:0>).

The HLVD module has an additional feature that allows

the user to supply the trip voltage to the module from an

external source. This mode is enabled when bits

HLVDL3:HLVDL0 are set to ‘1111’. In this state, the

comparator input is multiplexed from the external input

pin, HLVDIN. This gives users flexibility because it

allows them to configure the High/Low-Voltage Detect

interrupt to occur at any voltage in the valid operating

range.

FIGURE 21-1:

HLVD MODULE BLOCK DIAGRAM (WITH EXTERNAL INPUT)

Set

VDD

MUX

HLVDEN

HLVDCON

HLVDIN

HLVDL3:HLVDL0

Register

HLVDIN

VDD

Externally Generated

Trip Point

HLVDIF

HLVDEN

BOREN

Internal Voltage

Reference

VDIRMAG

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