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Modbus RTU vs Modbus ASCII: Frame Encapsulation, LRC Checks & Legacy Use Cases

Understanding Modbus ASCII: colon start characters, hexadecimal ASCII byte pairs, Longitudinal Redundancy Checks (LRC), and why RTU replaced it in modern plants.

  • Modbus ASCII requires twice the number of bytes as RTU to transmit the same data payload.
  • Modbus ASCII uses explicit start (':') and end ('CR/LF') delimiters, eliminating strict timing requirements.
  • Modbus ASCII is predominantly used on slow radio modems or acoustic telemetry links where continuous packet streaming cannot be guaranteed.

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