The Trigger Level defines when a signal changes state. In other words; if the voltage of a signal is inferior to the Trigger Level it will be regarded as 0 (Low), and vice versa. Similarly, when the signal voltage rises from below to above the Trigger Level, the LAP-F1 will consider that a change of state from Low to High has occurred and that the new state is 1 (High). The Trigger Level is sometimes referred to as Trigger Voltage or Threshold Level.
The LAP-F1 lets users use up to 4 different Trigger Levels at a time; one for each of the four port A, B, C and D. See the dialog box in figure 1.