3.3.4.3 AVR UPDI Interface

The Unified Program and Debug Interface (UPDI) is a Microchip proprietary interface for external programming and on-chip debugging of a device. It is a successor to the PDI two-wire physical interface, which is found on all AVR XMEGA devices. UPDI is a one-wire interface providing a bidirectional half-duplex asynchronous communication with the target device for purposes of programming and debugging.

Currently there are three configurations for UPDI:

  1. The UPDI function is on a shared pin that can also be used for RESET or GPIO. If RESET or GPIO has been selected and UPDI is now desired, an HV pulse is required on that pin to reactivate the UPDI functionality.

    This configuration is found on older AVR devices (ATtiny) and requires an HV pulse of 12V.

  2. The UPDI function is on a dedicated pin so UPDI is always available. RESET and GPIO share a pin.

    This configuration is found on newer AVR devices (ATmega0, AVR DA/DB etc.) and does not require an HV pulse.

  3. The UPDI function is on a shared pin that can also be used for GPIO. RESET is on a dedicated pin. If GPIO has been selected and UPDI is now desired, an HV pulse is required on the RESET pin to reactivate the UPDI functionality.

    This configuration is found on newer AVR devices (AVR DD) and requires an HV pulse of approximately VDD + 2 volts. See the device data sheet for the actual value range.

Consult your device data sheet for the configuration your device uses.