Display decoders — output polarity when the correct input is applied In most common LED/segment display decoders (e.g., BCD-to-7-segment with open-collector/sink outputs), when the correct input code is present the corresponding output line switches to which logic state?

Introduction / Context:
Many legacy and still-popular display decoders (such as the 74xx47 BCD-to-7-segment driver for common-anode displays) use active-LOW outputs that sink current to illuminate segments. Understanding the typical output polarity is essential for correct wiring and for avoiding inverted logic bugs during troubleshooting.

Given Data / Assumptions:

• Typical decoder with sink-capable outputs driving LEDs (often common-anode displays).
• Outputs are active-LOW: a LOW asserts the segment/line.
• Appropriate current-limiting resistors are assumed.

Concept / Approach:
In an active-LOW driver, asserting a particular output means pulling that line to LOW so current can flow from Vcc through the LED segment into the decoder output transistor to ground. Therefore, when the correct input code is applied, the related output line goes LOW to turn the target segment on (or to select the intended line in a decoder tree).

Step-by-Step Reasoning:

Verification / Alternative check:
Datasheets typically mark outputs with overbars (e.g., a, b, c with bars) or specify “active-LOW.” Bench tests with a current-limited supply confirm that a LOW at the output lights the intended segment on a common-anode display module.

Why Other Options Are Wrong:

• HIGH: would be active-HIGH behavior (common-cathode drivers), not typical of sink-type decoders.
• High impedance / open: tri-state behavior is not used for basic segment decode activation.
• Rapid toggling: not a normal decode response.

Common Pitfalls:

• Reversing display polarity (common-anode vs common-cathode) and getting inverted results.
• Omitting current-limiting resistors, which can damage segments even if logic polarity is correct.

Final Answer:
LOW