Cannot detect device with own JTAG cable

Hi acruvad.

I checked the signals both on the board and on the cable. I could see the signal on the cable but on the board, which I now know must have been down to the broken track.

I am still not sure about the cable though, as it didn't work earlier on a known working board even though I am pretty sure that was down to the wrong buffer IC.

Ideally I would be able to find some guidelines on the cables beyond the schematics, things like acceptable noise levels (I have some 100mv waveforms appearing when nothing else is driving the JTAG pins), decoupling requirements and maximum length, etc.

As you can probably tell this is the first time i've acctually needed to really think about JTAG.