a single conducting path provides communication between a jtag unit and a jtag tap controller . the data is communicated between the two units using time - division multiplexing . three time slots are allocated to data - in , to data - out and to jtag control signals . two of the time - division multiplexing slots exchange data by having one logic signal state defined by the supply voltage and the second logic signal state defined by the voltage level high than the supply voltage . the third time - division multiplexing slot has the logic signal state defined by the presence or absence of signal occurring within the time slot .