Detail of FTDI use

Other Hardware General Electronics
1

Hi,

I've been using a custom PCB with ATMega4809 MCUs and MegacoreX. I've just noticed that MCUDude's minimal set-up examples include a diode from RST to Vcc (scroll down in link above to the GitHub site) that I've never included before (with no troubles using serial uploads with Optiboot).

Can anyone explain to me (a) what benefit this diode would be, and (b) given that I've gotten consistent good results without it, under what circumstances might I expect to get into trouble unless I add it to my next revision?

Thanks,

Michael

2

https://github.com/MCUdude/MegaCoreX/issues/61#issuecomment-589952894

The diode prevents voltage doubling caused by the capacitor when the DTR pin toggles.

3

oh wow - thanks for the fast response!! This does sound worth including. The linked thread also includes mention of a 10k resistor, and MCUDude suggests he'd add it to his minimal set-up schematics, but it has not appeared. Can you tell me more about this?

edit: or is this 10k resistor just a standard pull-up on the reset pin, which I have already in any case?

4

Yes. Probably not needed because of the internal pull-up.