Get this frame from your serial monitor or logic analyzer after sending the built frame above to your device.
What is Modbus RTU?
Modbus RTU is a serial protocol for industrial automation. It uses compact binary frames for fast, reliable communication over RS-485 or RS-232. Each frame contains a device address, function code, data, and CRC16 checksum.
How does a frame work?
01
03
00 6B 00 01
F5 D6
Device address, function code, data, and CRC16. All values are bytes (0-255).
What is CRC and why does it matter?
CRC16 is a checksum that detects errors in the frame. The sender computes CRC16 over all bytes and appends it. The receiver recomputes and compares. If they don't match, the frame is discarded.
Master vs Slave explained
The master (your MCU/PLC) initiates all requests. Slaves (sensors, actuators) respond only when addressed. Up to 247 slaves can share one RS-485 bus.
Where do I get frames from?
Serial monitor, logic analyzer, or firmware debug logs. Use this tool to build frames to send, or decode frames you capture.