The basic block diagram of the conventional counter in its time interval mode of measurement is
shown in Figure 4. The main gate is now controlled by two independent inputs, the START input,
which opens the gate, and the STOP input which closes it. Clock pulses from the dividers are
accumulated for the time duration for which the gate is open. The accumulated count gives the
time interval between the START event and the STOP event. Sometimes the time interval may be
for signal of different voltage levels such as th shown in Figure 5. The input conditioning circuit
must be able to generate the START pulse at the 0.5V amplitude point, and the STOP pulse at the
1.5V amplitude point.