See the full article: https://www.avdweb.nl/arduino/attiny3217/ftdi-updi-connector Typically, debugging via the serial monitor and burning the bootloader requires 2 connectors: FTDI and UPDI (like the ICSP connector for the Atmega328 and others) These connectors, however, take up a lot of space on the pcb, especially with respect to the fact that the ATtiny devices, such as the ATtiny3217, are very small. That is why I have designed a new combined FTDI / UPDI connector, which take less space on the pcb.
avandalen/FDTI-UPDI-connector
Typically, debugging via the serial monitor and burning the bootloader requires 2 connectors: FTDI For debugging and uploading the sketch UPDI For burning the boot loader (like the ICSP connector for the Atmega328 and others) These connectors, however, take up a lot of space on the pcb, especially with respect to the fact that the ATtiny devices, such as the ATtiny3217, are very small. That is why I have designed a new combined FTDI / UPDI connector, which take less space on the pcb.
MIT