Hi, I have just started out with a 40 pin dip avr 4809 and used a circuit diagram I found at pyupdi https://github.com/mraardvark/py... (bottom of page) to create a updi programmer. Essentially it uses an FTDI board (in my case) and connects the Tx and Rx with a 4k7 resistor and the junction of Rx and the resistor is connected to the UPDI pin on the 4809. It works fine and I got the Microchip blinkled program uploaded and working (minor change req'd to code as no port B on the 40 pin chip).
So my question is I'd like to use the same FTDI board as UART comms with my serial monitor. I could introduce a couple of switches one to to break the lines connecting the Tx and Rx and one to break the UPDI line. ( I might try to use mosfets if I can work it out). That would free up the FTDI board when its not used for uploading, but then what about the state of the UPDI pin on the 4809? I thought I'd read the 4809 datasheet section 30 about UPDI and that made me realise I have led a sheltered life :) , so can I leave the UPDI pin floating when not in use or do I need to pullup / down (or none of these). Perhaps I'd be better off dedicating the FTDI board to the programming task and use another for the UART comms.
Although I've done a fair bit of programming over the years, my main electronics experience was working with valve guitar amps. They were nice and warm in winter...
thanks for help with the Q.