The logic analyzer has a fixed logic high voltage.
In that case you need a bit of extra help from some external circuits. Take a diode and resistor and put it series with the data line. Now data will only flow one way. So now repeat the arrangement but with the diode going the other way in parallel with the first diode and resistor.
Now you will get a voltage drop across one of the resistors when there is a high level, the resistor that you see the drop across will be dependent on the direction of the signal. This isn't a very big drop so to make it suitable for your logic analyser you need to wire a comparator across each of the resistors. You then have two signals to feed into the analyser, representing the two direction of travel of the signals.