That 100R is the ideal total source impedance but some of that will be provided by the processor pin. I did some extreme 1wire testing last year with a little test board with trimpot that let me hunt the best value for my cpu pin (an stm32 uart pin). I landed on 68R, but that’s not necessarily indicative of what the AVR would need.
One termination R trimpot for each bus.
Then you’ll need a very long bus to even see the reflection. I was dealing with hundreds of metres.
That Blue trace is the near end of the 1wire bus. The goal is to position that shelf on the initial falling edge so that it’s mid-way between high and low, and tweaking the pot moves it up and down. Then you can measure the pot and use that R value in your final design… 68R in my case.
On a much shorter bus, you probably won’t even see the reflection/shelf…
