60.4 External Reset Circuit

When the external Reset function is used, connect the external Reset circuit to the RESET pin as shown below. If the external Reset function is not required, the circuit is not necessary. The RESET pin can either remain unconnected, or be driven LOW externally by the application circuitry.

The Reset switch can also be removed if a manual Reset is not necessary. The RESET pin itself has an internal pull-up resistor, therefore it is optional to add any external pull-up resistor.

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, that is, 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.

Figure 60-7. External Reset Circuit Schematic
Note: Reset circuit recommendations to improve EFT/ESD/EMI immunity can be found in the “Basic 32-Bit MCU Design and Troubleshooting Checklist” guide avaialbe on the Microchip web site www.microchip.com/.
Table 60-2. Reset Circuit Connections
Signal NameRecommended Pin ConnectionDescription
RESETReset low level threshold voltage

VDDIO = 1.71V - 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 D5x/E5x features an internal pull-up resistor on the RESET pin, hence an external pull-up is optional.