What Is a Modbus IO Module?

The Founder's Explanation (Teach Exactly This Way)

"Courier delivers a parcel with only a number written on it — box 40001, box 40002. You must have the address book to know box 40001 is supply temperature, and multiply by point one. Without the book, it is just numbers. Modbus module is that courier. Register map is the address book. No book, no meaning."

Teaching the Concept

The Courier With Numbered Parcels A courier hands you parcels marked only with numbers — 40001, 40002, 40003. Without the address book that says what each number means, they are just boxes. A Modbus IO module speaks the same way: it hands over numbered registers, and the engineer must map and scale them. Read the map, apply the scale, and the raw number becomes a real value. The Register Map ``` Addr Type Point Scale 40001 Holding/Input Supply Water Temp x0.1 deg C 40002 Holding/Input Return Water Temp x0.1 deg C 40003 Holding Valve Command 0-1000 = 0-100% 10001 Discrete Pump Run Status 0/1 ``` What Decides Success ``` Transport Modbus RTU (RS485) or Modbus TCP (Ethernet) Framing slave address, baud, parity, stop bits Registers holding (read/write) vs input (read-only) Scaling apply x0.1; watch word order (endianness) ``` Modbus carries no meaning on its own — the register map is where raw numbers become real engineering.

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Related Topics

• What is Modbus and its history? — the simple register-based protocol
• Modbus to BACnet gateway explained — how a gateway translates protocols
• Browse all IO List & Wiring topics — more from this section of the EnSmart BMS Library