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Standard 8051 8-Bit Flash MCU
HT85F2260/HT85F2270/HT85F2280
Reset and Initialisation
Reset and Initialisation
RESET Pin Reset
For most applications a resistor connected between VDD and the RESET pin and a capacitor
connected between VSS and the RESET pin will provide a suitable external reset circuit. Any
wiring connected to the RESET pin should be kept as short as possible to minimise any stray noise
interference. For applications that operate within an environment where more noise is present the
Enhanced Reset Circuit shown is recommended.
RESET
VDD
0.1µF
Basic Reset Ci�c�it
100k
Ω
RESET
VDD
100k
Ω
0.1μF
10k
Ω
0.01μF
Enhanced Reset Circuit
This type of reset occurs when the microcontroller is already running and the RESET pin is
forcefully pulled low by external hardware such as an external switch. In this case as in the case
of other resets, the Program Counter will reset to zero and program execution initiated from this
point. Note that, during the power-up sequence, the reset circuit should make sure that the external
reset to be released after the internal power-on reset is over plus a suitable delay time. To improve
the noise immunity, the low portion of external reset signal must be greater than that specified by
t
RES
in the A.C. characteristics, for the internal logic to recognise a valid reset. When a RESET pin
reset takes place, the XRSTF bit in the RSTSRC register will be set high to indicate this reset.