Hi
I use the FT601 in my FPGA based design. I use 32bit bus with with 33R resistor for impedance matching on the bus (approx in the middle of the line since they are bidirectional).
Now
How can I read out the list of the combined lengths of the segment before and after this resistor?
How can I tune all those combined lengths to the longest of this combined length (I doesn’t matter if the resistor is exactly in the middle, however the combined length should be matched)
This is maybe a noob question (I am noob actually switched to kicad reacently from a comercial alternative): Sometimes when i manually did some trace editing. The length reporting is broken and doesn’t show the whole length?!? How to fix this?
I’m using version 7 so, video may not reflect your Version…
Call the Track’s Side A and Side B and say Side B is comprised of several Lengths and you want Side A’s length to match Side B’s length(?)
Know that Side A needs to be Long enough to fit the extra Length or, that you can tweak the Parameters to make it happen. Thus, I show it’s Not long enough to fit the length until I increased the Amplitude.
As far as getting Length data, a couple of ways to get the data - simplest is from the Net-Inspector. Thus, the Tracks need to be on a NET.
Can also use a Plugin (shown using my Plugin), Python-Code in the Command-Line Tool and/or can use the Measurement Tool as well as inspecting the data at bottom of the PCB Panel, lastly, you can Add (do the math) of individual segments…etc
Regarding Length Reporting… well, not a perfect world…
First: Thank you very much for your fast response, and the amount of effort you put in to make a clrear answer.
That makes me a bit ashamed since my Question was a bit confusing written:
What I mean is that I have a 32 bit bus with a resistor in the middle. So there are 32 A’s and 32 B’s. Lets call them A1, A2 … and B1, B2 etc.
So my goal is that the lenghs:
A1 + B1 = A2 + B2 = A3 + B3 … are equal. However I dont care much if A1 = B1 or not, just the sums as stated before needs to be identical.
Background is: This is the bidirectional FPGA ↔ FT601 interface. The CMOS driver of the chips has an output impedance in the range of 10-30 Ohms. My “non terminated” PCB traces have around 50Ohms. So I use a 33Ohm Resistor close to the driver, to “match” the impedance. The resistor also helps to damp reflections, so overall the signal quality should be improved using this resistor.
Now in this case the bus is bidirectional, so I place the resistor approximately in the middle (however this is not crucial to be precise so there is no A1 = B1 requirement).
All my nets have names. So the netinspector you have in your version would be extremely helpful. So the sums could be efficiently built manually. However I cant find It in my version (9)?
Regarding my prev. Question 3.: When move over a net with the “Tune lengh of single track (7)” tool activated it sometimes only measures the net partially (Especially when I prev. edited the traces manually).
Can manually set individual Segment Lengths as desired. Thus, can make both sides have the same Total Length. No Track Tuning required.
You state wanting both sides to have the same ‘total’ length and don’t care if A1 = B1. This makes it quick and easy to do it manually.
If for some reason you don’t want the same Quantity of Segments but do want the Same Total Length and Don’t want to do it Manually, then use the Tuning to make One-side equal the other side’s known length.
Example bellow shows Side B with Fewer Segments but having the Same Total length as Side A.
Then, it shows one with Shorter Side-B, copy/paste and Tuning Side-B to get desired length. Actually, I did Not bother to dial-in exact length but, you can do that (will need to tweak Grid and play with it…)
EDIT: Notice that I had set Side-B with the first two segments to be UnEqual but still having the same Total Length. Then, I shortened Side-B before Copy/Paste and Tuning…
To measure combined length before and after a resistor:
Go to PCB Editor > Inspect > Length Tuning > Select the Net (Bus line).
Manually add the lengths:
Click on the net from FPGA to resistor.
Then click on the net from resistor to FT601.
The two segments will show their lengths separately.
Sum them manually** to get the true length for matching.