HT85F2270 datasheet(76/226 Pages) HOLTEK

76 / 226 page

Rev. 1.00

76 of ��6

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Standard 8051 8-Bit Flash MCU

HT85F2260/HT85F2270/HT85F2280

24 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. A hardware reset will of course

be automatically implemented after the device is powered-on, however there are a number of other

hardware and software reset sources that can be implemented dynamically when the device is

running.

Reset Overview

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 instructions commence

execution. 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.

The devices provide several reset sources to generate the internal reset signal, providing extended

MCU protection. The different types of resets are listed in the accompanying table.

Reset Source Summary

No.

Reset Name

Abbreviation Indication Bit Register

Notes

1 Power-On Reset

POR

PORF

RSTSRC Auto generated at power on

� Reset Pin

RESET

XRSTF

RSTSRC Hardware Reset

� Low-Voltage Reset

LVR

LVRF

RSTSRC Low VDD voltage

4 LVRCR Register Setting Software

Reset

—

LRF

RSTSRC Write to LVRCR register

� Watchdog Reset

WDT

WDTS

IP0

Watchdog overflow

6 WDTCR Register Setting Software

Reset

—

WRF

RSTSRC Write to WDTCR register

7 �issing Clock Detection Reset

�CD

�CDF

RSTSRC To enable – set �CD bit in

�ISC register

8 Comparator 0 Output Reset

—

C�P0F

RSTSRC To enable – set CP0RST bit

in CP0CR register

9 SRST Register Setting Software

Reset

—

SRSTREQ

SRST

Write to SRST register

10 RO� Code Check Reset

—

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