1.1 Logic level
These are the voltages that represent the binary levels ‘0’ and ‘1’. Using
conventional logic (positive logic) binary ‘0’ is represented by a low voltage and binary
‘1’ by a higher (more positive) voltage.
The actual voltage levels are related to that voltage used to supply power to
the circuit. In TTL circuits the power supply (+Vcc) is +5 V ±5%, while CMOS systems will
work on supply voltages between 3.0 V and 18 V. The Figure 1-1 shows the logic level of
digital devices.