HT37B90 datasheet(34/80 Pages) HOLTEK

34 / 80 page

HT37B90/HT37B70/HT37B50/HT37B30

Rev.1.00

June22,2017

· LowVoltageReset

- LVR

The microcontroller contains a low voltage reset cir-

cuit in order to monitor the supply voltage of the de-

vice, which is selected via a configuration option and

The VLVR can select as 3.0V or 2.4V. If the supply

voltage of the device drops to within a range of

0.9V~VLVR such as might occur when changing the

battery, the LVR will automatically reset the device in-

ternally. The LVR includes the following specifica-

tions: For a valid LVR signal, a low voltage, i.e., a

voltage in the range between 0.9V~VLVR must exist for

greater than the value tLVR specified in the A.C. char-

acteristics. If the low voltage state does not exceed

1ms, the LVR will ignore it and will not perform a reset

function.

· WatchdogTime-outResetduringNormalOperation

The Watchdog time-out Reset during normal opera-

tion is the same as a hardware RES pin reset except

thattheWatchdogtime-outflagTOwillbesetto

²1².

· WatchdogTime-outResetduringPowerDown

The Watchdog time-out Reset during Power Down is

a little different from other kinds of reset. Most of the

conditions remain unchanged except that the Pro-

gram Counter and the Stack Pointer will be cleared to

²0² and the TO flag will be set to ²1². Refer to the A.C.

Characteristicsfor tSST details.

ResetInitialConditions

The different types of reset described affect the reset

flags in different ways. These flags, known as PDF and

TO are located in the status register and are controlled

by various microcontroller operations, such as the

Power Down function or Watchdog Timer. The reset

flagsareshowninthetable:

TO PDF

RESETConditions

RES resetduringpower-on

RES or LVR reset during normal operation

RES Wake-upHALT

WDT time-out reset during normal operation

WDT time-outresetduringPowerDown

Note:

²u² standsforunchanged

The following table indicates the way in which the vari-

ous components of the microcontroller are affected after

apower-onresetoccurs.

Item

ConditionAfterRESET

ProgramCounter

Resettozero

Interrupts

Allinterruptswillbedisabled

WDT

Clear after reset, WDT begins

counting

Timer/Event

Counter

TimerCounterwillbeturnedoff

Prescaler

The Timer Counter Prescaler will

becleared

Input/OutputPorts I/Oportswillbesetupasinputs

StackPointer

Stack Pointer will point to the top

ofthestack

The different kinds of resets all affect the internal regis-

ters of the microcontroller in different ways. To ensure

reliable continuation of normal program execution after

a reset occurs, it is important to know what condition the

microcontroller is in after a particular reset occurs. The

following table describes how each type of reset affects

eachofthe microcontroller internalregisters.

L V R

S S T T i m e - o u t

I n t e r n a l R e s e t

t R S T D

LowVoltageResetTimingChart

W D T T i m e - o u t

S S T T i m e - o u t

I n t e r n a l R e s e t

t R S T D

WDT Time-outResetduringNormalOperation

TimingChart

W D T T i m e - o u t

S S T T i m e - o u t

t S S T

WDT Time-outResetduringPowerDown

TimingChart

R E S

S S T T i m e - o u t

I n t e r n a l R e s e t

0 . 9 V D D

0 . 4 V D D

t R S T D

RES ResetTimingChart

HT37B90 Datasheet(PDF) 34 Page - Holtek Semiconductor Inc

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