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A small circle on a lead marking active-low behaviour.
Also known as: Active low bubble, Negation circle, Inversion circle
A small circle where a lead meets a symbol marks that connection as inverted or active-low. On an output it means the signal is negated; on an input it means the function is triggered by a low rather than a high, and a reader who ignores it inverts the logic of the whole drawing.
Marks a connection as inverted, whether an output that is negated or an input that is active when low.
Contexts: Technical drawing, Electrical equipment
Is the single most consequential small mark in a digital schematic, because ignoring one inverts the logic of everything downstream.
Contexts: Technical drawing, Electrical equipment
A small hollow circle placed where a line meets the body of a symbol.