Arduino UNO and Nano CH340G Schematics

[anon35827816]

@anon35033284

I don't really understand this

It's explained in the datasheet of every ATMega processor. In short, if you apply a voltage around 12V to the Reset pin, the chip enters a programming mode that's normally not accessible that allows for instance fuses to be reprogrammed that are normally write-once.

@anon35033284

So, should I route them side by side or not?

Yes. That's what I meant by saying "It's common to route them side by side."

[anon35033284]

Ok, thxx

[anon35033284]

@anon35827816

keep noisy traces (e.g. power supply) as far away from them as realistically possible

Is GND included in the "power supply" category?

[anon35827816]

No, although more strictly speaking I should say 'it depends', but given your schematic, just go with 'no'. It's OK to route such lines close to GND.

[anon35033284]

What will happen if my USB DATA- is a little longer than the USB DATA+

My DATA+ length is 9.325mm (BottomLayer)-Via Diameter (1mm) Hole (0.5mm)- 2.121mm (TopLayer)

My DATA- length is 13.419mm (BottomLayer)-Via Diameter (1mm) Hole (0.5mm)- 2.398mm (TopLayer)

[anon35827816]

@anon35033284

What will happen if my USB DATA- is a little longer than the USB DATA+

There may be transfer errors and/or a failure of the USB chip to be recognized correctly & consistently.

You can introduce some angles in the shorter trace (DATA+) in order to make it longer.

Btw, usually there is no impact of such a small length difference, but when laying out a new PCB, there's no need to take the risk, IMO.

[anon35033284]

Okayy

[anon35033284]

Now:
My DATA+ length is 13.424mm (BottomLayer)-Via Diameter (1mm) Hole (0.5mm)- 2.121mm (TopLayer)

My DATA- length is 13.419mm (BottomLayer)-Via Diameter (1mm) Hole (0.5mm)- 2.398mm (TopLayer)

I can't make it closer than that...

[anon35033284]

Will that be gud?

[anon35827816]

I don't think it gets any better than that!

[anon35033284]

So its still bad?

[anon35033284]

Oh ok, now it can be the same length (13.418mm)

[anon35033284]

@anon35827816

I've had an occasional problem with a microcontroller going into high-voltage programming mode due to a very short discharge peak on its Reset pin. A diode (pretty much any kind will do) with its anode to reset and cathode to Vcc solves the problem.

What's the most common diode to do this job?

[anon35033284]

I often see a diode near the icsp headers
but no markings there..
Just black background with a white strip to indicate the cathode

[anon35033284]

@anon35827816

In short, if you apply a voltage around 12V to the Reset pin, the chip enters a programming mode that's normally not accessible that allows for instance fuses to be reprogrammed that are normally write-once.

If I power my board only using 9v-jack and USB, do I still need to add the diode?

[anon35827816]

Any small signal diode will do. I often use MBR0520, but 1n4148 for instance would do just fine as well.

@anon35033284

If I power my board only using 9v-jack and USB, do I still need to add the diode?

Doesn't matter where the power comes from.

[anon35033284]

The point is, that I won't use any 12v input

[anon35827816]

@anon35827816

Doesn't matter where the power comes from.

I'll say it again...

[anon35033284]

Can I do that with a Digital Pin's Net?
(Combine 2 tracks to one just like on the pic)

[anon35827816]

If they're the same net, yes.