Cable length limitation for SPI run at 40MHz ???

[AShiu.1]

I had trouble to activate SPI communication with SPI in 40MHz frequency in 55cm long cable , even I modified output speed to "Very high speed" . Is any other register that I need to set to support high speed clock in long length cable ? 55cm long cable is not possible to support 40MHz ,?

[TDK]

A 55cm cable is pretty long for 40MHz single ended SPI. I would not expect it to work okay without attention to impedance matching and proper terminations. It's not a matter of chip support, it's a matter of signal integrity in the cable, after the signal leaves the chip.

A differential signal in a shield cable would do better (e.g. USB).