In digital electronics and computer systems, various codes are used to represent numbers and characters. The question asks about a specific code where each decimal digit is represented by a group of 4 binary bits. Let's explore the given options to identify the correct code.

Binary Coded Decimal (BCD) Explained

Binary Coded Decimal (BCD) is a system where each decimal digit (0 through 9) is represented by its own 4-bit binary equivalent. This means that for a decimal number like 23, the '2' would be represented by its 4-bit binary code (0010), and the '3' would be represented by its 4-bit binary code (0011). The complete BCD representation of 23 would then be 0010 0011.

The key characteristic of BCD is that it uses a fixed group of 4 bits to represent each individual decimal digit. This makes it easy for digital circuits to interface with decimal displays and perform decimal arithmetic, which is often required in applications like calculators, digital clocks, and financial systems.

Understanding Other Digital Codes

Let's briefly examine the other options to understand why they do not fit the description:

• Gray Code: Gray code is a non-weighted code, meaning that the bit positions do not have specific weights (like 8, 4, 2, 1 in binary). It is unique because only one bit changes between successive numbers. This property is useful in preventing errors in digital-to-analog converters and position encoders, but it does not represent each decimal digit using a unique 4-bit group independent of its position or other digits in a number.
• Excess-3 Code: Excess-3 code is a self-complementing, non-weighted BCD code. It is derived by adding binary \(\text{0011}_2\) (decimal 3) to each 4-bit BCD code. While it uses 4 bits per decimal digit, it's a specific variation of BCD, not the fundamental definition of a code where each decimal digit is represented by 4 binary bits. The primary code for this direct representation is BCD itself.
• ASCII Code: ASCII (American Standard Code for Information Interchange) is primarily an character encoding standard. It uses 7 or 8 bits to represent characters like letters (uppercase and lowercase), numbers, punctuation marks, and control characters. For example, the ASCII code for the character '1' is \(\text{00110001}_2\) (49 in decimal), which is 8 bits, not 4 bits, and it represents the character '1', not the numerical value 1 in a specific 4-bit group per decimal digit.

Identifying the Correct Code

Based on the definitions, the code in which each decimal digit is represented by a group of 4 binary bits is precisely the definition of BCD (Binary Coded Decimal). This makes BCD the correct answer for the given question.