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Topic: Changed auto reset R/C values for the UART together with UPDI for the ATtiny3217 (Read 1 time) previous topic - next topic

avandalen

The following applies to the ATtiny XMEGA microcontroller series.
If an Arduino ATtiny3217 requires an USB serial interface for programming and debugging and also an UPDI connector for burning the bootloader, this has consequences for the auto reset circuit. The autoreset R/C circuit is required for the serial USB interface. The used R/C values are normally 10k / 100nF, but these values are no longer usable in combination with a UPDI connector. I have figured out that 100k / 10nF works well and does not disturb the UPDI operation.
I have tested that the minimum value of the resistor is 40kOhm which not disturbs the UPDI.
A value of 100k seems to me to be a safe value.
The voltage drop due to the maximum input current of 1uA is 0.1V.
See this article:
https://www.avdweb.nl/arduino/misc/ftdi-updi-connector

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