HT85F2240 datasheet(67/147 Pages) HOLTEK

67 / 147 page

Rev. 1.10

67 of 147

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A/D Flash 8051 Core Low Pin Count MCU

HT85F2230/HT85F2240

23 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

Notes

1 Power-On Reset

POR

PORF

RSTSRC A�to generated at power on

� Reset Pin

RESET

XRSTF

RSTSRC Hardware Reset

� Low-Vo�tage Reset

LVR

LVRF

RSTSRC Low VDD vo�tage

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 SRST Register Setting

Software Reset

—

SRSTREQ

SRST

Write to SRST register

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