36.3.2.1.2 UPDI Enable with High-Voltage Override of UPDI Pin

An application can configure the UPDI pin as an I/O pin. In this case, the regular one-wire enable sequence cannot be used.

An HV pulse applied to the RESET pin will switch the pin functionality of the UPDI pin to the UPDI function.

  1. Apply the HV signal, as described in Figure 36-6 and the Electrical Characteristics section. The HV must be applied after the POR has been released.

    This will override the pin configuration of the UPDI pin. The HV detection circuitry will trigger a device Reset. The CPU will remain halted until the reception of a valid UPDI key, or the expiration of TUPDI_TIMEOUT. If no such key is received, the device will be reset and the UPDI pin will have the configuration specified by the fuses.

  2. Follow the regular one-wire enable sequence as described in 36.3.2.1.1 One-Wire Enable. A valid UPDI key must be sent before TUPDI_TIMEOUT.
  3. When the UPDI is enabled by an HV pulse, only a POR will disable the override of the UPDI pin and restore the settings as configured by the fuses.
Figure 36-6. UPDI Enable Sequence by High-Voltage (HV) Programming
Note:
  1. If insufficient external protection is added to the UPDI pin, an ESD pulse can be interpreted by the device as a high-voltage override and enable the UPDI.
  2. The actual threshold voltage for the UPDI HV activation depends on VDD. See the Electrical Characteristics section for more details.
  3. See the Electrical Characteristics section for the value of TUPDI_TIMEOUT.