Do you start in a simulator?

[rx8pilot]

It isn't much of an exaggeration to say everything is analogue, with the exception of femtoamp circuits (counting individual electrons) and avalanche photodiodes (counting individual photons). "Digital" circuits are merely analogue circuits where the voltages/currents are interpreted to represent (usually) binary signals.

A couple of years ago when I was introduced to high-speed digital - this reality hit me like a ton of bricks! I made a few devices that have serial bit rates at 3Gbps, 6Gbps, and 12Gbps with edge rates at a few 10's of picoseconds. It is definitely all analog in that domain. The software needed to simulate that type of digital signal is a few notches above LT Spice.

[tggzzz]

for anything io , digital , microcontroller and simple analog : straight to board.

Only for simple stuff.

It is highly educational to simulate a multi-output digital system driving a moderate load. To pick a few figures:

• a digital output, say 3V, with a series 100ohm resistor, 1ns risetime
• one side of that digital output is connected to an inductor to ground. That inductor represents the inductance of the ic's ground lead, 1nH/mm so say 5nH
• that resistor is connected to a transmission line, 100ohms, 1ns, and the other end of the transmission line is connected to a 5pF capacitor representing another ic's input capacitance

Do a transient analysis and look at both ends of the transmission line.

Then simulate eight such outputs switching simultaneously, by reducing the resistor to 12.5ohms.

If you think that is academic, I suggest you look at and understand the IBIS models published for digital ics - and why they need to exist.

Why would you want to do that ? That is bad design practice to begin with.

Beginners should do it to get a gut feel for why it is indeed bad practice. The OP is a beginner, and many beginners can read this thread in the future.

So you aren't a beginner; shrug.

The driving IC output is already in the order of 20 to 25 ohms. So you are  mismatching your transmission line.
1nS rise time is NOT a GPIO of a microcontroller anymore. Your run of the mill micrcontroller can't even go there. Besides those are current limited and slope controlled these days.

The last jellybean IC I measured was ~7ohms, and had transition time of <1ns (not <1nS).

A beginner probably wouldn't even notice the drive strength settings.

If i need to make a controller for let's say a reflow oven or a plant watering system : there is no need to grab a simulator. that's straight to board.

You seem to have missed my starting with "Only for simple stuff.". That is simple stuff.