Data Communication and Transmission: A Comprehensive Overview

Posted on Nov 24, 2024 in Electronics

1. DTE and DCE: Definition and Examples

DTE (Data Terminal Equipment)

Acts as the source or destination of data and manages communication control. Examples include terminals and computers.

DCE (Data Circuit-terminating Equipment)

Adapts the digital signal to the transmission medium’s characteristics. Examples include routers and modems.

2. Parallel vs. Serial Transmission

Parallel Transmission

Advantage: High speed, potentially increasing transfer rate by a factor of n.

Disadvantage: High cost due to requiring n communication lines, limiting its use to short distances.

Serial Transmission

Advantage: Lower cost compared to parallel transmission due to using a single communication channel.

Disadvantage: Requires conversion devices (parallel-to-serial and serial-to-parallel) at the interfaces.

3. ASCII: American Standard Code for Information Interchange

A 7-bit code representing 128 alphanumeric characters. Often extended to 8 bits with an additional parity bit (b7) for error detection. Widely used in data transmission.

4. ASCII Code Division

Divisions are in groups of four. Example: 16hex = 0001 0110bin = 22dec

5. Source Code Definition

A set of text lines containing instructions that a computer follows to execute a program.

6. Purpose of Source Code

Provides the instructions that a computer must execute to run a specific program.

7. Communication Types

Simplex

Unidirectional communication where the sender and receiver are fixed. Commonly used in broadcast networks.

Half-Duplex

Bidirectional communication where both ends can transmit and receive, but not simultaneously. Often used in terminal-computer interactions.

Full-Duplex

Bidirectional communication where data flows simultaneously in both directions. Requires different frequencies or separate communication paths.

8. Synchronous vs. Asynchronous Transmission

Asynchronous Transmission (Start/Stop)

Uses start and stop bits to signal the beginning and end of each character.

Synchronous Transmission

Requires transmitter and receiver to share the same clock frequency. Data is transmitted in blocks with delimiters marking the start and end.

9. Extra Bits in Asynchronous Transmission

1 start bit and 1 stop bit.

10. Point-to-Point vs. Multipoint Transmission

Point-to-Point

Example: A computer connected to a printer.

Multipoint

Example: A local area network with multiple computers connected to a router.

11. Modulation

The process of superimposing a low-frequency information signal (modulating signal) onto a high-frequency carrier signal.

12. Carrier and Modulating Signals

Carrier Signal: The high-frequency signal that carries the information.

Modulating Signal: The low-frequency signal containing the data.

13. FSK Modulation

Frequency-shift keying (FSK) is a digital modulation technique where different frequencies represent binary values (0 and 1).

14. AM vs. FM Modulation Advantages

AM (Amplitude Modulation)

Less susceptible to noise fading, making it suitable for mobile and air/ground communications.

FM (Frequency Modulation)

Offers higher quality audio and video, commonly used in radio and television broadcasting.

15. HART Protocol

Enables bidirectional digital communication with smart instruments without interrupting the 4-20mA analog signal.

16. HART Protocol Advantages over 4-20mA

The digital signal uses frequencies of 1200Hz and 2200Hz to represent binary values, superimposed on the 4-20mA current loop without affecting the analog signal.

17. Pulse Width Modulation (PWM)

A technique that modifies the duty cycle of a periodic signal to transmit information or control power delivery.

Duty Cycle (D) = τ / T, where τ is the pulse width and T is the period.

PWM circuits typically use a comparator with a triangular wave oscillator and a modulating signal input.

Disadvantage: Potential for radio frequency interference.

18. Multiplexing Types

Time Division Multiplexing (TDM)

Transmits multiple channels over a single circuit by dividing the time into slots.

Frequency Division Multiplexing (FDM)

Transmits multiple channels simultaneously by dividing the frequency spectrum into smaller bandwidths.

19. Line Coding

Enables transmission of digital signals over various media by encoding each data bit into a signal element.

20. Manchester vs. NRZ Coding

Manchester Coding

A self-synchronizing method with a transition between signal levels for each bit.

NRZ (Non-Return-to-Zero) Coding

Assigns a voltage level to each symbol, simplifying encoding but not self-clocking.

21. RS232 vs. RS422

RS232

  • Logic High: -3V to -15V
  • Logic Low: +3V to +15V
  • Max Cable Length: 15m
  • Max Speed: 9600Kbps

RS422

  • Logic 0: 1.5V to 5V
  • Logic 1: -1.5V to -5V
  • Max Cable Length: 1200m
  • Max Speed: 10Mbps

22. RS232, RS422, and RS485 Characteristics

RS232

  • Max Speed: 9600Kbps
  • Impedance: 7KΩ
  • Voltage: High (-3V to -15V), Low (+3V to +15V)
  • Max Distance: 15m

RS422

  • Max Speed: 10Mbps
  • Impedance: 4KΩ
  • Voltage: 0 (1.5V to 5V), 1 (-1.5V to -5V)
  • Max Distance: 1200m

RS485

  • Max Speed: 10Mbps
  • Impedance: 12KΩ
  • Voltage: -7V to 12V
  • Max Distance: 1200m

23. Balanced Transmission

Uses line voltage comparison to determine logic levels (e.g., RS422 and RS485).

24. Characteristic Speed of RS232

Commonly used at speeds up to 9600Kbps.