5cm isn’t that long, one of my clock lines is probably close to double that. In the photo of the MAX6960 Controller board above the two termination resistors are the two 33 Ohm resistors just above the black connector on the bottom left of the board.
You need to make sure you have a good, short path (ie low inductance ground connection) for the clock signal and return current to flow in, ideally running right next to each other. Make sure your oscillator and MAX6960 devices are well decoupled (100nF capacitors on every VCC pin) and the addition of some bulk capacitance (a couple of ~10uF or so electrolytics or tantalums) across VCC can’t hurt either.

I got my circuit working on prototype board using mostly wire-wrap connections. The key is to keep your connections as short as possible and think about how the return current will flow through the ground connections and keep that path as short as possible too, within reason.

The important thing to remember with high speed digital design is that there are much higher frequency harmonics in the clock signal than just the fundamental clock frequency, and these are the ones that will cause you trouble.
And big current loops = big trouble, unless you are building an antenna!

Your termination resistor contraption sounds interesting. Could you please provide a schematic? (ascii drawing is sufficient ) are they just in series with the cable going from clock’s output to osc input?

Anyhow, my cable running from the oscillator output to the 2nd board is just 5cm long. Is that already enough for noisy oscillator lines? unfortunately, i don’t have an oscilloscope to dig more into it!
thanks for your help so far

This is to try and keep the clock clean (ie prevent ringing etc). I initially ran the clock through two gates of a buffer IC to produce two individual clocks with series termination resistors, but my wire wrap construction technique wasn’t up to the job and it made all the other signals on the buffer IC noisy.

The termination resistors are to dampen any ringing on the line by trying to match the characteristic impedance of the clock signal wires. The value of 33 ohms is a best guess, anything from 22 to 100 ohm should work.
Don’t forget that the clock also has to be 3.3V for the MAX6960! I used a 5V part but found it worked ok at 3.3V.

The display I built uses a 8.10018 MHz oscillator module, it’s just what I had on hand at the time. If you use a different clock you need to change the frequency in the max6969x_conf.h file in the Library I posted. Then delete the .o file in the library directory and recompile your code.

The data sheet says that anything from 1MHz to 8.5MHz will do for a clock. The frequency you choose only effects the maximum and minimum frame rates if you operate in automatic memory plane switching mode. Just make sure you use a 3.3V clock.

I will eventually put up more detailed information about the display I built and better instructions about how to use the library… only so many hours in a day!

could you please update which Clock Rate you used for the the Max6960?

It would be also very helpful, if you could post your arduino code for the scrolling text example!

thanks again!