17.4 External Reset Circuit

The external reset circuit should be connected to the RESET pin when the external reset function is used. If the external reset function has been disabled, the circuit is not necessary. The reset switch can also be removed, if the manual reset is not necessary. The RESET pin itself has an internal pull-up resistor, hence it is optional to add any external pull-up resistor.

Figure 17-5. External Reset Circuit Schematic

A pull-up resistor makes sure that the reset does not go low and unintentionally causing a device reset. An additional resistor has been added in series with the switch to safely discharge the filtering capacitor, i.e. preventing a current surge when shorting the filtering capacitor which again can cause a noise spike that can have a negative effect on the system.

Table 17-3. Reset Circuit Connections
Signal Name Recommended Pin Connection Description
RESET Reset low level threshold voltage

VDDIO = 1.6V - 2.0V: Below 0.33 * VDDIO

VDDIO = 2.7V - 3.6V: Below 0.36 * VDDIO

Decoupling/filter capacitor 100nF(1)

Pull-up resistor 10kΩ(1)(2)

Resistor in series with the switch 330Ω(1)

 Reset pin

1. These values are only given as a typical example.

2. The SAM R30 features an internal pull-up resistor on the RESET pin, hence an external pull-up is optional.