Just noticed this thread now ... haven't had much time to post here due to a rush home renovation job that'll keep me occupied for another 8-12 weeks or so.
Yes, the 1K pullup on the UPDI pin will create an issue with both the 12V pulse and regular UPDI programming. It needs to be temporarily disconnected.
Your diagram is quite pixelated when zooming in so a better image or perhaps a pdf attachment would help in viewing the part numbers.
The HVUPDI programmer has a built-in 1.2K series resistor, so its best to connect directly to the target UPDI (PA0) wthout any additional series resistor.
It looks like you have an OLED display connected. If the SCL and SDA lines have pullups, this might interfere with the required power cycle, so I think the best HV programming method would be automatically just after power-up.
There are 2 points in time when the programmer sends the 12V pulse.
- Immediately after power-up
- Just after performing its own power-cycle on the T5V power signal.
Let's focus on being able to power your board by using just the true 5V power and GND (hopefully this can be done). If so, then you can use PCHV mode and connect:
- The direct 5V power from the programmer's 6-pin header to target VCC (do not use T5V).
- Direct connection of UPDI to target PA0
- GND to target GND
With this method, the power-cycle is actually the power-up of the programmer and target board. The 5V power from the programmer's 6-pin header is more robust and should be able to power up your board c/w OLED.