Definitions for Digital Systems

Combinational circuit







The output is determined by the combinations of one or more inputs


Sequential circuit






Output is dependent on:

      The current input to the circuit;

      The previous inputs to the circuit.







Changes in output do not occur immediately there is a change in input, but the next time there is a clock pulse









The next stage is triggered by the completion of the previous stage without reference to a clock pulse







Level triggering in which the changes occur when the level of the pulse is either at 0 or 1.

Edge triggering in which the change occurs as the clock pulse rises from 0 to 1(rising or positive edge) or from 1 to 0 (falling or negative edge).






Edge triggered devices are called flip-flops.






Level sensitive devices are often referred to as latches