HT67F488 datasheet(53/171 Pages) HOLTEK

53 / 171 page

Rev. 1.60

�ove��e� �� 016

HT67F488/HT67F489

TinyPowerTM A/D Flash MCU with LCD & EEPROM

Low Voltage Reset — LVR

Themicrocontrollercontainsalowvoltageresetcircuitinordertomonitorthesupplyvoltageofthe

device.TheLVRfunctionisalwaysenabledwithaspecificLVRvoltageVLVR.Ifthesupplyvoltage

ofthedevicedropstowithinarangeof0.9V~VLVRsuchasmightoccurwhenchangingthebattery,

theLVRwillautomaticallyresetthedeviceinternallyandtheLVRFbitintheCTRLregisterwill

alsobesetto1.ForavalidLVRsignal,alowsupplyvoltage,i.e.,avoltageintherangebetween

0.9V~VLVRmustexistforatimegreaterthanthatspecifiedbytLVRintheLVD&LVRElectrical

Characteristics.Ifthelowsupplyvoltagestatedoesnotexceedthisvalue,theLVRwillignorethe

lowsupplyvoltageandwillnotperformaresetfunction.TheactualVLVRvaluecanbeselectedby

theLVSbitsintheLVRCregister.IftheLVS7~LVS0bitsarechangedtosomecertainvaluesby

theenvironmentalnoiseorsoftwaresetting,theLVRwillresetthedeviceafteradelaytime,tSRESET.

Whenthishappens,theLRFbitintheCTRLregisterwillbesetto1.Afterpowerontheregister

willhavethevalueof01010101B.NotethattheLVRfunctionwillbeautomaticallydisabledwhen

thedeviceentersthepowerdownmode.

LV R

In te r nal R es et

t RS TD + t SST

Note:tRSTDispower-ondelay,typicaltime=50ms

Low Voltage Reset Timing Chart

• LVRC Register

Bit

�a�e

LVS7

LVS6

LVS5

LVS4

LVS3

LVS�

LVS1

LVS0

R/W

POR

Bit7~0

LVS7~LVS0:LVRvoltageselect

01010101:2.1V

00110011:2.55V

10011001:3.15V

10101010:3.8V

Anyothervalue:GeneratesMCUreset--LVRCregisterisresettoPORvalue

Whenanactuallowvoltageconditionoccurs,asspecifiedbyoneofthefourdefined

LVRvoltagevaluesabove,anMCUresetwillbegenerated.Theresetoperation

willbeactivatedafterthelowvoltageconditionkeepsmorethanatLVRtime.Inthis

situationtheregistercontentswillremainthesameaftersucharesetoccurs.

Anyregistervalue,otherthanthefourdefinedLVRvaluesabove,willalsoresultin

thegenerationofanMCUreset.Theresetoperationwillbeactivatedafteradelay

time,tSRESET.HoweverinthissituationtheregistercontentswillberesettothePOR

value.

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