BCD-to-Seven-Segment — Why a Code Converter Is Needed In a BCD-to-seven-segment display system, why must a dedicated code-converter/driver be used between the 4-bit BCD source and the seven display segments (a–g)?

Introduction / Context:
A seven-segment display requires specific segment patterns for each decimal digit. A 4-bit BCD input encodes digits 0–9 but does not directly drive segments. A BCD-to-seven-segment code converter (often integrated with a driver) translates the 4-bit code into seven control lines to illuminate the correct segments.

Given Data / Assumptions:

• Input: 4-bit BCD representing 0–9.
• Output: seven control signals for segments a–g.
• Display type: common anode or common cathode (affects active level but not the need for conversion).

Concept / Approach:
The mapping from each BCD value to segments is a truth table (e.g., digit 2 lights a, b, g, e, d). A converter implements this logic and may also provide current limiting, blanking, lamp test, and ripple-blanking features. Without conversion, the raw BCD lines cannot produce correct segment combinations.

Step-by-Step Solution:
Identify inputs: 4 BCD bits → 10 valid combinations.Identify outputs: 7 segment control lines.Define mapping: each digit 0–9 maps to a unique 7-bit pattern.Therefore, a code converter is needed to translate BCD into the required 7-bit segment code.

Verification / Alternative check:
ICs such as 7447/7448 implement the conversion. Their datasheets provide the BCD-to-segment truth tables confirming the necessity of conversion.

Why Other Options Are Wrong:

• 10-bit code: Seven-segment displays need 7 outputs, not 10.
• Gray code: Unrelated to segment driving.
• No conversion: Contradicts the required mapping from digits to segments.

Common Pitfalls:
Confusing common-anode vs common-cathode drive polarities; the converter may output active-LOW or active-HIGH levels accordingly.

Final Answer:
to convert the 4-bit BCD into 7-bit code