/sɪˈkwɛnʃəl ˈsɜːrkɪt/
noun … “Logic circuit whose output depends on current and past inputs.”
Sequential Circuit is a type of digital logic circuit in which the output depends not only on the present input values but also on the circuit’s history or previous states. Unlike combinational circuits, sequential circuits incorporate memory elements such as flip-flops or latches to store state information, enabling complex behaviors like counting, timing, and controlled sequencing.
Key characteristics of Sequential Circuit include:
- State dependency: output depends on both current inputs and stored state.
- Memory elements: flip-flops, latches, or registers store past information.
- Clocked operation: often synchronized with a clock signal to update state predictably.
- Deterministic behavior: follows state transition rules defined by logic and memory.
- Applications: counters, shift registers, finite state machines (FSMs), control units, and pipelines in CPUs.
Workflow example: Simple 2-bit counter using flip-flops:
clock_signal = generate_clock()
counter_state = 0b00
for tick in clock_signal:
counter_state = (counter_state + 1) & 0b11 -- increment modulo 4
output(counter_state)
Here, the output depends on both the incoming clock signal and the previous counter state, demonstrating sequential logic.
Conceptually, a Sequential Circuit is like a combination lock: the current output depends not only on the dial’s present position but also on the sequence of previous positions.
See Combinational Circuit, Flip-Flop, Digital, Finite State Machine, CPU.