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DIFFERENT WAYS TO RESET ST7 MICROCONTROLLER

3 EXTERNAL RESET

A reset signal originating from an external source is one of the ways in which you can reset the

microcontroller. This signal must have a duration of at least the External reset pulse hold time,

can enter reset state even in Halt mode.

There are several reset implementation schemes to choose from based on your application-

specific parameters, such as power supply behaviour. Whatever the solution chosen, the idea

is to keep the RESET pin at a low logic level until the supply has reached a safe operating

voltage. Therefore you should design your external circuit in such a manner that there is

3.1 RCD Circuit

This concept is the simplest, most cost-effective external reset solution where the supply

waveform is monotonous and the maximum rise time is known. The principle is to let the

RESET pin rises with the MCU supply voltage after a delay. The circuit is shown in Figure 2.

The basic solution is to use an RC delay determined by the rise rate of the supply itself. The

component values must be chosen to create enough delay to keep the RESET pin below the

stant) corresponding to at least 30% of the total rise time is generally advised.

Figure 2. RCD Circuit

This scheme requires a certain delay between a power-down and next power-up, because the

delay generator has to be re initialized. In practice, a pull-down capacitor between RESET and

sequent power-up, should it occur soon after the power down (the delay required is reduced).

The difference in the discharge time of the Capacitor with and without the diode is significant

from Figure 3.

1

2

C

RESET

D

R