I recently ordered a UCD90SEQ64EVM-650 board for developing with the UCD90124A. On the board I have, R9 and R10 were both installed. This shorts the TCK and TRCK pins. My cable was unable to 'overdrive' the clock pin, so the JTAG clock had a high voltage of approx. 1V. According to the schematic here: http://www.ti.com/lit/ug/slvu423/slvu423.pdf R10 is not supposed to be populated. After removing R10 I was able to scan the JTAG chain correctly and the JTAG TCK pin looks as I expect.