CHAPTER 9 Digital Signals Voltage Levels Definition A digital signal is one in which a change in voltage, and the time at which it occurs, are of very much more importance than the precise size of the change or the exact shape of the waveform. All of the waveforms used in digital circuits are steep-sided pulses or square waves and it is the change in voltage that is significant, not the values of voltage. For that reason, the voltages of digital signals are not referred to directly, only as 1 and 0. The important feature of a digital signal is that each change is between just two voltage levels, typically 0 V and þ5 V, and that these levels need not be precise. In this example, the 1 level can be anything from 2.4 V to 5.2 V, and the 0 level anything from 0 V to þ0.8 V. We could equally