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UART Communication Explained: Baud Rate, Data Frame, Common Issues

UART Communication Explained: Baud Rate, Data Frame, Common Issues

UART Communication Explained

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UART (Universal Asynchronous Receiver/Transmitter) is the most commonly used serial communication method and the core interface for serial HMI displays.

1. How UART Works

UART is asynchronous communication that doesn't require a clock signal. Transmitter and receiver synchronize through a preset baud rate.

Basic Wiring:

  • TX (Transmit) → RX (Receive)
  • RX (Receive) → TX (Transmit)
  • GND → GND

2. Baud Rate

Baud rate determines data transfer speed in bps (bits per second).

Common Baud Rates:

  • 9600bps: Low speed, best stability
  • 115200bps: Recommended balance
  • 921600bps: High speed, short distance

GPT LCM Default: 9600bps or 115200bps

3. Data Frame Structure

A standard UART data frame contains:

  1. Start bit (1 bit): Low level, data begins
  2. Data bits (5~8 bits): Actual data
  3. Parity bit (0/1 bit): Error detection (optional)
  4. Stop bit (1/1.5/2 bits): High level, data ends

Common Config: 115200, 8, N, 1

4. Common Issues

Screen not responding:

  • Check TX/RX crossover
  • Confirm baud rate match
  • Check power supply

Garbled display:

  • Baud rate mismatch
  • Data/stop bit config error
  • Signal interference (use shielded cable)

Unstable communication:

  • Lower baud rate
  • Shorten distance
  • Add termination resistor (RS485)

5. Best Practices

  1. Use 115200bps for balanced speed/stability
  2. Shielded cables for industrial environments
  3. 120Ω termination resistors at RS485 bus ends
  4. Always connect common ground