What is Modbus RTU CRC checksum?
Modbus RTU uses CRC-16 (Cyclical Redundancy Check) for error detection. It's a 2-byte checksum calculated from all bytes in the frame except the CRC itself, helping ensure data integrity during transmission. See also our calculate Bandwidth to Data Rate.
How is the CRC-16 calculated in Modbus RTU?
The CRC-16 uses polynomial 0xA001 (reversed 0x8005). The calculation starts with 0xFFFF, processes each data byte, and the final result is appended as low byte first, then high byte.
What are the timing requirements for Modbus RTU?
Modbus RTU requires a silent interval of at least 3.5 character times between frames. For baud rates ≤19200, use exact 3.5 character calculation. For higher rates, use minimum 1.75ms.
What is the difference between character interval and frame interval?
Character interval is the time between individual bytes (1.5 character times max), while frame interval is the silent time between complete frames (3.5 character times minimum).
How do I format input data for the calculator?
Enter hex bytes separated by spaces (e.g., '01 03 00 00 00 0A'). Don't include the CRC bytes as they will be calculated automatically.
What happens if I use different baud rates?
Higher baud rates reduce transmission time but require more precise timing. Rates above 19200 bps use fixed minimum intervals instead of character-time calculations.