Why the 10cm limit on programming cable used with nRF54L15 DK to program custom board?

[Ken58]

Hi,

I was able to purchase a commercially available 30cm ribbon cable to connect from the nRF54L15 DK to a custom board for programming.  I later realized the DK documentation specifies a maximum 10cm cable for this function.  Why is this restriction necessary, and how would I expect programming to fail if I use a 30cm cable?

Thank you,

Ken

[PaKa]

The drivers on the DK doesn't support driving the signal through longer cables, the impedance doesn't work out. You will probably see the programming fail if you use a too long cable.

[Ken58]

Hi PaKa,

Can you explain that for someone without an electrical engineering background?

Thanks,

Ken

[Turbo J]

HF black magic weakens signals over longer cables. How long too long is depends on the signal itself.

And you want the debug signals to run as fast (and thus as high) as possible. 

TL;DR Use a short debug cable.