Seven-segment displays — behavior of a common-anode LED module A seven-segment, common-anode LED display is designed for which control behavior?

Introduction / Context:
Seven-segment LED displays come in two wiring polarities: common-anode and common-cathode. Understanding their behavior is necessary when selecting driver ICs or building microcontroller interfaces, because the logic level required to illuminate a segment depends on the common node connection.

Given Data / Assumptions:

• Common-anode type: all anodes of the segments are tied together internally.
• The common anode is typically connected to Vcc through a current-limiting path.
• Individual segment pins are the cathodes.

Concept / Approach:
For a common-anode display, to turn a segment ON you must sink current from its cathode to ground (logic LOW at the driver output). Conversely, applying a logic HIGH to the cathode stops current flow, turning the segment OFF. This is the opposite of common-cathode displays, where a logic HIGH at the segment pin lights the LED.

Step-by-Step Reasoning:

Verification / Alternative check:
Consult a typical driver like the 74xx47 BCD-to-7-segment decoder for common-anode displays; its outputs are active-LOW, matching the sink-current requirement. A quick bench test with a resistor confirms that LOW lights a segment and HIGH turns it off.

Why Other Options Are Wrong:

• All cathodes wired together: describes common-cathode devices.
• One common LED: each segment is its own LED; there is no single common LED.
• Disorientation of modules: not a technical behavior.
• A HIGH to turn on each segment: opposite of common-anode behavior.

Common Pitfalls:

• Forgetting current-limiting resistors; each segment typically needs its own resistor.
• Using a source-only driver with a common-anode module; a sink-capable driver is preferred.

Final Answer:
a HIGH to turn off each segment