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DIFFERENT WAYS TO RESET ST7 MICROCONTROLLER

Figure 3. Waveform of Power-on-Reset with RCD Circuit (Without MCU)

On ST7 there are internal protection diodes on the pads, which would solve the purpose of this

external diode, thereby you could do away with this diode in your actual implementation with

the MCU. The waveform of Power-on Reset with the External RC Circuit connected to ST7

without the diode is shown in Figure 4.

Figure 4. Waveform of Power-on-Reset with RC Circuit (With MCU)

One consideration when choosing the values of the resistor and capacitor is to ensure that re-

sistor’s value does not get too high and interfere with the ability to drive RESET pin high given

the worst case leakage current of the pin. Higher resistor values in the order of Mega Ohms

tion. The capacitor should not be too large when using MCU’s that have an active internal

reset because this could mask the Internal reset. So, a proper combination of component

values is required. Because of this limitation of selecting higher component values, this solu-

Without Diode - Capacitor discharges

very slowly

With Diode - Capacitor discharges

quickly

RESET

RESET

R=47K, C=10uF

,

VDD risetime = 1250msec/5V