Found this one: Adafruit UPDI Friend - USB Serial UPDI Programmer : ID 5879 : Adafruit Industries, Unique & fun DIY electronics and kits
If you ave ATtiny1604 MCU, try to program it using Arduino as ISP. The conection is same as above. Read data sheet to see which pins have the alternate functions for MOSI. MISO, and SCK.
I suggest that you buy one and explore the options for programming based on information from the data sheet and the author of the Arduino core. You will discover that UPDI is a completely different concept and that you can't simply use any programming method that you choose.
Are you suggesting an experiment to test whether the programming information in the data sheet is wrong?
If the additional memory is not program you could use an external FRAM but that would require at least two connections for I2C. The ones I use are 32K x 8.
Do you think so?
I've not tried it but it looks good for programming chips like the attiny1604 which use UPDI.
Ok so! Thanks for all your helps, really appreciate
So I will buy:
Adafruit UPDI Friend (13€ with shipping)
These may also be useful:
I don't want to weld them, I want to move them on different board. But thanks