Definition
Digital electronic circuits whose output depends not only on the current input signals but also on the previous state of the circuit. Sequential logic devices contain memory elements (such as flip-flops) that store the prior state, allowing the circuit to produce outputs based on a sequence of inputs over time rather than just the present input.
Plain English
Electronic circuits that remember what happened before. Their output depends on both the current signal and what the circuit was doing a moment ago. They are the building blocks of counters, registers, and timing circuits inside aircraft computers.
Context Anchor
Seen in discussions of digital avionics, electronic control circuits, counters, timers, and memory-based aircraft systems.
Derivation
Sequential comes from the Latin sequi, meaning 'to follow.' The name fits because the circuit's output follows a sequence -- each step depends on the one before it, not just the present input.
Why Pilots Care
Sequential logic is the foundation of nearly every digital system in a modern cockpit -- from flight management computers to transponders. Understanding that these circuits have memory helps explain why some avionics need a power-cycle reset to clear an unwanted state.
Analogy
A light switch is simple because its result depends only on its present position. A sequential logic device is more like an elevator controller: it must know which floor it is on, which button was pressed, and what step comes next.
Intuition Check
Do not read sequential logic devices as simply electronic parts placed one after another. The key idea is memory: the device’s output depends on both the current signal and a previous condition.
Example Sentence 1
Counters and registers inside the flight computer are built from sequential logic devices, which is why they can keep track of pulses over time.
Example Sentence 2
The navigation unit uses sequential logic devices to track changes in heading over successive updates.