probing internal signal

If this is a high speed internal signal, you can't view it "live" unless you bring all the signals out to a bench oscilloscope or other suitable equipment. As noted, Signal Tap takes a snapshot based on a trigger you set up. Signal Probe only brings out one signal at a time. You could use In-System Sources & Probes (ISSP) but that only updates at the speed of the JTAG clock, so using it for a high speed signal is out of the question.

If you need to look at this whole bus live, use the LAI (Logic Analyzer Interface) tool to bring the whole bus out of the device.