comments on the schematic and PCB about sduino_uno HOT 3 CLOSED

Thanks for the constructive comments! I appreciate them a lot.

In order:

• The STM8S105 devices, among others, have an integrated ROM bootloader that briefly listens for programming data on all UART and SPI ports, provided that the program flash is empty or the respective option byte is set. SWIM programming should therefore never be needed, except for mishaps where the bootloader enable option has accidentally been disabled. In that case the board can still be flashed via jumper wires. I therefore chose to omit a dedicated SWIM header.
• Damnit! Thanks a lot! Of course it is supposed to connect the way you pointed out.
• Neither the Arduinos nor their clones have that, but I'll take it into consideration.
• Yes, J2 just replaces the solder bridge found on the Arduino. You can cut the reset line on the bottom side where the arrows are and solder on a jumper header. That way J1 and J2 can be left unpopulated by default.
• That part of the circuit has been taken from the Arduino reference design without modification, so I consider it well tested.

The USB to CH340G wiring is taken from the CH340G application notes and is largely identical to that found on the (admittedly CE-less) Arduino clones. So for now (10 piece prototype run), I'd consider additional EMC and ESD measures unnecessary gold plating.

Concerning PDFs: I might upload PDFs once I have working boards. No need to spam the git history.

PCB:

• There already is a GND ring around Y2, C5, C6, D2, C11 and C4 that connects to pin 4. It goes through half a dozen VIAs but should be better than nothing.
• The VIA should be below the solder mask.
• The placement of the I2C lines is clearly not optimal, indeed. It was the best routing I could come up with, though. Let's hope that possible 16MHz interference does not harm the 100kHz signal too much. If it does, one might have to switch to the internal 16MHz resonator.
• Maybe I'll flip C2. There is not much more I can do without starting over.

I did consider using a smaller resonator. Most of them look next to impossible to hand-solder, though. That is why I went for the common HC49-THT type. They are also much cheaper (in volume) and easier to source.

And once again thank you for pointing out that major TX/RX brain fart! That could have resulted in a great deal of disappointment and frustration.

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Ok, that all makes sense. I wasn't aware of the build-in bootloader. Hopefully, we will not miss the SWIM connector more often then expected.

I just added support for this proposed pin mapping in the new experimental branch of sduino, but since I don't have any similar CPU it is completely untested. Feedback would be highly appreciated!

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I think we can close this.

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