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Standard 8051 8-Bit Flash MCU
HT85F2260/HT85F2270/HT85F2280
Reset and Initialisation
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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 Powe�-On Reset
POR
PORF
RSTSRC A�to gene�ated at powe� on
� Reset Pin
RESET
XRSTF
RSTSRC Ha�dwa�e Reset
3 Low-Voltage Reset
LVR
LVRF
RSTSRC Low V
DD
voltage
4 LVRCR Registe� Setting Softwa�e
Reset
—
LRF
RSTSRC W�ite to LVRCR �egiste�
� Watchdog Reset
WDT
WDTS
IP0
Watchdog overflow
6 WDTCR Registe� Setting Softwa�e
Reset
—
WRF
RSTSRC W�ite to WDTCR �egiste�
7 Compa�ato� 0 O�tp�t Reset
—
CMP0F
RSTSRC To enable – set CP0RST bit
in CP0CR �egiste�
8 SRST Registe� Setting Softwa�e
Reset
—
SRSTREQ
SRST
W�ite to SRST �egiste�
9 ROM Code Check Reset
—
—
—
—