Connection for RESET

The RESET pin on the device is active-low with an internal pull-up resistor, and externally pulling the pin low will result in a device Reset. An external pull-up resistor is usually not required.

The following figure shows the recommendation for connecting an external Reset switch to the device.

Figure 1. Recommended External Reset Circuit Schematic

Shorting the filtering capacitor may cause a noise spike that can harm the system. To prevent this, a resistor in series with the switch can safely discharge the filtering capacitor preventing a current surge.

UPDI Enable with High-Voltage Override

It is possible to enable a disabled UPDI by applying a high-voltage pulse on the RESET pin. Take care with the reset circuit design and any components connected to the RESET pin to prevent damage if such a high-voltage pulse may be applied.

See the Connection for UPDI Programming sub-section and the UPDI section for more details.