HT67F60 datasheet(71/242 Pages) HOLTEK

71 / 242 page

HT67F30/HT67F40/HT67F50/HT67F60

TinyPowerTM A/D Flash Type 8-Bit MCU with LCD & EEPROM

Rev. 1.50

March 06 , 2012

Rev. 1.50

March 06 , 2012

8- st age Di vi der

f S

WD T Ti me - out

(2 8 /f S ~ 2 15 /f S )

f S /2 8

WD T Pr e sca le r

8- to -1 M U X

Cl ear W DT T yp e

C onf i gur at i on Op ti on

CL R WD T1 F la g

CL R WD T2 F la g

1 or 2 I ns tr uc ti ons

CL R

f SU B

WS 2~ WS 0

( f S /2 8 ~ f S /2 15 )

f SY S /4

LX T

LI RC

C onf i gur at io n

O p ti on

C onf i gur at io n

Op ti on

Watchdog Timer

Reset and Initialisation

A reset function is a fundamental part of any microcontroller ensuring that the device can be set to

some predetermined condition irrespective of outside parameters. The most important reset

condition is after power is first applied to the microcontroller. In this case, internal circuitry will

ensure that the microcontroller, after a short delay, will be in a well defined state and ready to

execute the first program instruction. After this power-on reset, certain important internal registers

will be set to defined states before the program commences. One of these registers is the Program

Counter, which will be reset to zero forcing the microcontroller to begin program execution from the

lowest Program Memory address.

In addition to the power-on reset, situations may arise where it is necessary to forcefully apply a

reset condition when the is running. One example of this is where after power has been applied and

the is already running, the RES line is forcefully pulled low. In such a case, known as a normal

operation reset, some of the registers remain unchanged allowing the to proceed with normal

operation after the reset line is allowed to return high.

Another type of reset is when the Watchdog Timer overflows and resets the . All types of reset

operations result in different register conditions being setup. Another reset exists in the form of a

Low Voltage Reset, LVR, where a full reset, similar to the RES reset is implemented in situations

where the power supply voltage falls below a certain threshold.

Reset Functions

There are five ways in which a reset can occur, through events occurring both internally and

externally:

● Power-on Reset

The most fundamental and unavoidable reset is the one that occurs after power is first applied to

the . As well as ensuring that the Program Memory begins execution from the first memory

address, a power-on reset also ensures that certain other registers are preset to known conditions.

All the I/O port and port control registers will power up in a high condition ensuring that all pins

will be first set to inputs.

RE S

VD D

In te r nal R es et

0. 9 V DD

t RS TD + t SST

Power-On Reset Timing Chart

Note: tRSTD is power-on delay, typical time=100ms

HT67F60 Datasheet(PDF) 71 Page - Holtek Semiconductor Inc

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