Which description best defines a BCD display?

• A. A binary-coded decimal system that uses groups of 4 bits to represent decimal digits
• B. A decimal display using four-digit blocks
• C. A hexadecimal display
• D. A number system that uses groups of 4 digits to represent decimal values

Answer: (C)

BCD encoding represents each decimal digit with its own 4-bit group, a nibble. This means a decimal number like 42 would be stored or displayed as two nibbles: 0100 for the digit 4 and 0010 for the digit 2. Keeping digits in separate 4-bit blocks lets a driver easily map each nibble to the appropriate decimal digit and drive a display (often via a seven-segment decoder) digit by digit. In standard BCD, only the patterns 0000 through 1001 are valid for digits 0–9; patterns 1010–1111 aren’t used for digits unless special handling is added.

This is different from a hexadecimal display, which uses each 4-bit nibble to represent 0–F (0–15) in hex, not decimal. The description that mentions four-bit groups for decimal digits captures the essence of how BCD operates, whereas the other descriptions don’t specify the per-digit 4-bit encoding used to represent decimal values.