Digital Codes Overview

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Questions and Answers

What is the Excess-3 code for the decimal digit 5?

  • 1100
  • 1000
  • 1011 (correct)
  • 1001

Which of the following codes is specifically designed to represent decimal digits using exactly two bits set to 1?

  • 2-out-of-5 code (correct)
  • Gray code
  • Self-Complement code
  • Excess-3 code

What is the primary characteristic of Gray code?

  • Every combination differs by two bits
  • It has four bits for each decimal digit
  • Only one bit differs between successive values (correct)
  • It's a weighted code

In a 2-out-of-5 code, how many unique combinations can represent decimal digits?

<p>10 (C)</p> Signup and view all the answers

What is the binary representation of the decimal number 4 in Excess-3 code?

<p>1001 (B)</p> Signup and view all the answers

Which of the following codes aids in error correction for digital communications?

<p>Gray code (C)</p> Signup and view all the answers

What operation commonly uses a shift count code in programming?

<p>Bit manipulation (D)</p> Signup and view all the answers

Which code has a property where no digit representation has more than one bit difference?

<p>Gray code (B)</p> Signup and view all the answers

What is a characteristic of weighted codes?

<p>Each digit has a specific weight based on its position. (B)</p> Signup and view all the answers

Which of the following codes is self-complementing?

<p>Reflective codes (D)</p> Signup and view all the answers

How many bits are required in BCD to represent a number with 3 decimal digits?

<p>12 bits (B)</p> Signup and view all the answers

What is the binary representation of the decimal number 185 in BCD?

<p>0011 1001 0110 (B)</p> Signup and view all the answers

Which of the following statements about BCD is correct?

<p>Numbers from 0 to 9 are the only valid representations in BCD. (C)</p> Signup and view all the answers

What defines sequential codes?

<p>Each succeeding code is greater than the last. (B)</p> Signup and view all the answers

What is the primary function of error detecting and correcting codes?

<p>To allow for identification and rectification of errors. (A)</p> Signup and view all the answers

Which of the following is NOT a type of digital code?

<p>Reflection Codes (A)</p> Signup and view all the answers

What is the purpose of parity bits in error-detecting codes?

<p>They help identify errors in data. (C)</p> Signup and view all the answers

Given the blocks 1011 and 0001, how is the first block expanded to a 7-bit representation?

<p>The fourth bit is determined by $b5 + b6 + b7$ being even. (B)</p> Signup and view all the answers

How is the parity bit P1 calculated in the 8-bit data structure?

<p>P1 is the XOR of D3, D5, D7, D9, and D11. (A)</p> Signup and view all the answers

What does BCD stand for in alphanumeric codes?

<p>Binary Coded Decimal (B)</p> Signup and view all the answers

What range of characters can be represented using the standard BCD code?

<p>64 characters (B)</p> Signup and view all the answers

In parity bit error detection, if bits 1 and 2 are incorrect, where is the error likely to occur?

<p>In bit 3 only. (C)</p> Signup and view all the answers

What is the characteristic of the minimal bit representation for standard alphanumeric codes?

<p>It can express one character using 6 bits. (C)</p> Signup and view all the answers

What is the maximum number of characters that can be represented in ASCII code?

<p>128 characters (B)</p> Signup and view all the answers

Which of the following correctly describes the EBCDIC code?

<p>Uses 8 bits for character representation (A)</p> Signup and view all the answers

Which of the following represents a common error when understanding error detection?

<p>Not recognizing that error detection is different from error correction. (D)</p> Signup and view all the answers

In ASCII, which bit is considered the parity bit for advancements in error-checking?

<p>Bit 7 (B)</p> Signup and view all the answers

Identify the correct statement regarding the characters represented in EBCDIC code.

<p>It includes lowercase letters, numbers, and special characters. (C)</p> Signup and view all the answers

Which hexadecimal code represents the carriage return (CR) in ASCII?

<p>0D (D)</p> Signup and view all the answers

What does the term 'zone bit' in ASCII refer to?

<p>It denotes the type of character being used. (A)</p> Signup and view all the answers

What character does the binary value 0001 in EBCDIC represent?

<p>Start of Heading (SOH) (B)</p> Signup and view all the answers

Which of the following correctly describes the difference between EBCDIC and ASCII?

<p>ASCII is primarily used on personal computers, while EBCDIC is used on mainframes. (A)</p> Signup and view all the answers

What is a key advantage of using Gray Code in numerical representation?

<p>Only one bit changes between two consecutive numbers. (C)</p> Signup and view all the answers

Which of the following correctly describes the function of a parity bit?

<p>It ensures that the total number of 1's is either even or odd. (A)</p> Signup and view all the answers

What is the minimum number of parity bits required when encoding a message of 4 data bits using Hamming code?

<p>3 parity bits (B)</p> Signup and view all the answers

How does the addition of multiple parity bits affect communication efficiency?

<p>It may lead to decreased efficiency. (D)</p> Signup and view all the answers

In Hamming code, what does the relationship '$d \geq 5$ and $d \leq 11$' indicate?

<p>The threshold for the number of parity bits needed. (C)</p> Signup and view all the answers

Which of the following best explains why Hamming code uses even parity?

<p>It simplifies the error detection process. (B)</p> Signup and view all the answers

What does the notation 'p' represent in the context of error-detecting codes?

<p>The number of parity bits. (D)</p> Signup and view all the answers

Which operation is used to convert between Binary and Gray codes?

<p>XOR (⊕) (A)</p> Signup and view all the answers

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Study Notes

Digital Codes: Overview

  • Digital data is represented and processed as a group of bits, also known as a binary code.
  • Weighted codes: Each digit has a specific weight based on its position.
  • Non-weighted codes: Digits are not positionally weighted.
  • Reflective codes: The code for a digit is the complement of the code for its inverse (for example, the code for 9 is the inverse of the code for 0).
  • Sequential codes: Each code is one binary value higher than the previous code.
  • Alphanumeric codes: These represent numbers, alphabet characters, and symbols.
  • Error-detecting and correcting codes: Detect errors in data communication and processing.

Numeric Codes

  • BCD (Binary Coded Decimal): A number with k decimal digits requires 4k bits.
    • Example: Decimal 396 represented in BCD is 0011 1001 0110 (12 bits).
    • Each group of 4 bits directly corresponds to one decimal digit.
    • The binary combinations 1010 through 1111 are not used in BCD.
  • Excess-3 code: BCD code + 0011.
    • It also has a self-complementing characteristic.
  • Other Non-weighted Codes:
    • 2-out-of-5 code: Each decimal digit is represented by 5 bits, with exactly two bits set to 1 and the rest set to 0.
    • Shift count code: Describes the number of bit shifts in a binary number. Used for tasks like bit manipulation.
    • Gray code: A system where two successive values differ in only one bit. Useful for error detection and analog-to-digital conversion.

Gray Code Properties

  • Only one bit changes between successive values.
  • Used in Analog to Digital Converters (ADCs) for error detection and reducing power consumption.

Error-Detecting Codes

  • Parity: An extra bit (parity bit) is added to make the total number of 1s in a message either even or odd.
  • Hamming Code: Uses multiple parity bits to detect and correct single-bit errors.
    • Number of bits n needed for error detection/correction is related to the number of data bits d:
      • 2 ^(n-1)-n+1 <= d <= 2 ^(n-1)-n-1.
    • Example: 4 parity bits are required if you have 5 to 11 data bits.

Hamming Code Implementation

  • Parity bits are placed at positions 1, 2, 4, 8, and so on, depending on the location of the parity.
  • Data bits fill the remaining locations.

Alphanumeric Codes

  • Standard BCD Code: Expresses one character using 6 bits.
    • Maximum of 64 characters can be represented.
    • Used in specialized digital systems.
  • EBCDIC (Extended Binary Coded Decimal Interchange Code): Uses 8 bits to represent characters.
  • ASCII (American Standard Code for Information Interchange):
    • Uses 7 bits (128 unique characters) for personal computers, and often 8 bits (with added parity) for communications.
    • Each character is divided into a zone bit and a digit bit.

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