Digital Codes Quiz

Study Notes

Digital data is represented, stored and transmitted as groups of binary digits also known as binary code.
Weighted codes: Each digit is assigned a specific weight according to its position.
Non-weighted codes: Codes not appositionally weighted.
Reflective codes: The code is self complementing.
Sequential codes: Each succeeding 'code is one binary number greater than its preceding code.
Alphanumeric codes: Codes used to represent numbers, alphabetic characters, symbols
Error defecting and correcting codes: Codes which allow error defection and correction are called error detecting and correcting codes.

Numeric Codes
- Binary Coded Decimal (BCD): Each decimal digit is represented by a 4-bit binary code.
- A decimal number in BCD is the same as its equivalent binary number only when the number is between 0 and 9.
- Other Decimal Codes
- Gray Code: Only one bit changes between two consecutive codes.
  - Useful for analog-to-digital conversion, error detection and low power design.
Error-Detecting Codes
- Parity: An extra bit is added to a message to make the total number of '1's either even or odd.
- Hamming Code: Uses multiple parity bits to detect and correct errors.
  - It can detect and correct one-bit errors in a data block.
  - The number of parity bits needed depends on the number of data bits.
Alphanumeric Codes
- Standard BCD Code: Uses 6 bits to represent a character, up to 64 characters.
  - Used in specific digital systems.
- Extended Binary Coded Decimal Interchange Code (EBCDIC): Used primarily on IBM medium and large computers.
  - Uses 8 bits to represent a character, up to 256 characters.
- American Standard Code for Information Interchange(ASC-II): Used on personal computers.
  - Uses 7 bits to represent a character, up to 128 characters.
  - For communications, it uses 8 bits with an added parity bit.

Can detect and correct a single bit error using parity bits
Parity bits are positioned at powers of 2 (1, 2, 4, 8, ...)
Parity bits are calculated by XORing the data bits they cover.
To detect errors.
- Calculate the parity bits for the received data
- If any parity bits don't match the original, an error has occurred
- The number of parity bits that are incorrect gives the location of the error.

Parity Checking: Detects errors by checking if the number of '1's is even or odd.

Uses a 6-bit structure:
- 1 zone bit
- 5 digit bits.
Supports characters from A to I (0001~~1001), J to R (0001~~1001), S to Z (0010~~1001), 0 to 9 (0001~~1010), and other special characters.

Uses an 8-bit structure:
- 1 parity bit
- 4 zone bits
- 4 digit bits
It is used on IBM mainframes.
It includes a wide range of characters, including control characters, special characters, lowercase letters, uppercase letters, and numeric digits.

Most common character encoding system used today.
It uses a 7-bit structure:
- 1 parity bit
- 3 zone bits
- 4 digit bits
Supports characters from 0 to 9, a to z, A to Z, and various special characters.