HT85F2240 datasheet(66/147 Pages) HOLTEK

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Rev. 1.10

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A/D Flash 8051 Core Low Pin Count MCU

HT85F2230/HT85F2240

22 Low Voltage Detector – LVD

Each device has a Low Voltage Detector function, also known as LVD. This enables the device

to monitor the power supply voltage, VDD, and provide an interrupt should it fall below a certain

level. This function may be especially useful in battery applications where the supply voltage will

gradually reduce as the battery ages, as it allows a battery low early warning signal to be generated.

The LVD function can also generate an interrupt signal if required.

LVD Register

The Low Voltage Detector function is controlled using a single register with the name LVDCR.

Three bits in this register, LVDS2~LVDS0, are used to select one of eight fixed voltages below

which a low voltage condition will be determined. The LVDEN bit is used to control the overall on/

off function of the low voltage detector. Setting the bit high will enable the low voltage detector.

Clearing the bit to zero will switch off the internal low voltage detector circuits. As the low voltage

detector will consume a certain amount of power, it may be desirable to switch off the circuit when

not in use, an important consideration in power sensitive battery powered applications.

LVDCR Register

SFR Address: EBh

Bit

Name

LVDEN

—

LVDS�

LVDS1

LVDS0

R/W

—

R/W

POR

—

Bit 7

LVDEN: LVD Function Control

0: Disable

1: Enable

Bit 6~3

Unimplemented, read as “0”

Bit 2~0

LVDS2 ~ LVDS0: Select LVD Voltage

000: 2.0V

001: 2.2V

010: 2.4V

011: 2.7V

100: 3.0V

101: 3.3V

110: 3.6V

111: 4.2V

LVD Operation

The Low Voltage Detector function operates by comparing the power supply voltage, VDD, with

a pre-specified voltage level stored in the LVDCR register. This has a range of between 2.0V and

4.2V. When the power supply voltage, VDD, falls below this pre-determined value and if the LVD

interrupt function is enabled, the LVD interrupt will take place and the interrupt request flag,

LVDF, in the IRCON2 register, will be set high. The LVDF bit will be cleared to low by hardware

automatically. The LVD interrupt can cause the device to wake-up from the IDLE Mode. If the

Low Voltage Detector wake up function is not required then the LVDF flag should be first set high

and disable the LVD interrupt function before the device enters the IDLE Mode. When the device

is powered down the low voltage detector will be disabled to reduce the power consumption.

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