Tool/software:
Hello experts,
My customer asked how the reflection on RS-485 signal would look like, waveform-wise. May I ask how it would look?
I was able to find below image from below apps note, but does this mean that it would only decrease in magnitude?
I was a bit confused, as when I googled 'reflection rs-485', second image showed mostly distortions from reflections.
https://www.ti.com/document-viewer/lit/html/SSZTB23
Thank you in advance for your help and support.
Hi jade,
Reflections can actually look very different from one scopeshot to another.
I've added a few below as an example. The main signals shown are the A-B math signal:
This one the signal hangs close to GND. before it begins transitioning which distorts the bit time of the signal.
You can see in this one, the signal on the bottom is A-B which are a bit more acceptable.
The blue signal below is also one that seems like it's not too bad though the signal transitions start getting a bit slow
Below, the signal looks non monotonic at the higher and lower points but it's no where near the Vth+ and Vth- levels so it shouldn't cause any bit errors.
Yellow below is A-B but for LVDS, this could still be an RS485 signal in theory. The reflections in this signal were to due a lot of nodes and longer stubs at high data rate and moderate distance. This one below looks like signal integrity could be at risk.
Essentially, reflected signals can look completely different depending on the system and where you probe the signal.
-Bobby
