Digital logic uses the boolean logic represented with high and low voltage values: depending on what voltage represents the /true/ value the logic is active high or active low.

With technology improvement the voltage ranges used to represent logic level has changed

Technology L Voltage H Voltage Notes
CMOS 0V to 1/3VDD 2/3 Vdd to Vdd Vdd = supply voltage
TTL 0V to 0.8V 2V to Vcc Vcc = 5 +/- 10%

Combinatorial logic

Sequential logic


Tri-state logic

  • Tri-state logic: Connecting multiple outputs together - 8 bit register - Part 2 video
  • Making logic gates from transistors video