4.4.2 UPDI Connection v2
This connection is compatible with any AVR device but requires an adapter cable for users with older programmers/debuggers, such as the Atmel-ICE and the Atmel PowerDebugger with the 100-mil 2x3 header connector. This connection is directly compatible with the PICkit™ 4 In-Circuit Debugger programming tool.
The UPDI Connection v2 uses a 100-mil 4-pin 1x4 header. Although three pins are sufficient for programming many AVR devices, it is recommended to use a single-row 100-mil 4-pin header to allow inclusion of the RESET signal. This connector is also compatible with the PICkit 4 programmer.
The following figure shows the recommended method for connecting a UPDI connector to the device.
The decoupling capacitor between VDD and GND must be placed as close to the pin pair as possible. Include the decoupling capacitor even if the UPDI connector is not included in the circuit.
Enabling UPDI Using RESET
By design or by mistake, it may be possible to disable UPDI by writing to the appropriate fuse. For details on disabling UPDI, see the FUSE - Configuration and User Fuses section of the Memories chapter. Note that for devices with a dedicated UPDI pin, there is no fuse to disable UPDI.
A high-voltage pulse must be applied to the RESET pin to re-enable UPDI. See the UPDI - Unified Program and Debug Interface chapter for details on how to apply the high-voltage pulse to the RESET pin.
Take additional care in the circuit design if the RESET pin is connected to other components. If a high-voltage pulse is applied to the RESET pin, other components connected to the line might be damaged. In this case, the design must allow these components to be disconnected from the circuit before the high-voltage pulse is applied. One example is a removable jumper.