Introduction to Sequential Logic

Output is determined by the current state and the input. The output is fed back to the input to determine the next output.

Clock

Generates a series of pulses at regular intervals. Used to synchronize the operation of digital circuits.

Clock signal

A square wave with a 50% duty cycle. The signal is high for half the period and low for the other half.

Triggering methods

Determines when the output changes according to the clock signal.

Positive edge-triggered

Output changes on the rising edge of the clock signal.

Negative edge-triggered

Output changes on the falling edge of the clock signal.

Level Triggering

Output changes when the clock signal is high (or low).

Characteristics

Characteristic table

A table of memory, current input and output. Similar to a truth table.

Excitation table

A table used to determine the required inputs for a sequential circuit element to transition from its current state to a desired next state. Provides a mapping between the current state, next state, and the necessary inputs. Essential for designing and analyzing sequential circuits.

Latch & Flip-flop

A memory element that can store a bit.

Latch

Level triggered. Independent of a clock.

Flip-flop

Edge triggered. Dependent on a clock.

Types of sequential circuits

Asynchronous

Works without a clock. Built using latches.

Synchronous

Works based on a clock. Built using flip flops.