How does Modbus protocol work

[King123]

I'm reaching out to gain a better understanding of the Modbus protocol in a general sense. Although I haven't specified a particular microcontroller or Modbus device, let's consider a scenario.

Suppose I have a microcontroller and two Modbus devices - Device A (Relay) with an address of 0x10 and register address 0x11, and Device B (Temperature sensor) with an address of 0x20 and register address 0x21. The communication interface is RS485.

My objective is for the microcontroller to read data from the temperature sensor and control the relay using the Modbus protocol. In a basic Modbus RTU frame, there's a start bit, slave address, function code, data, CRC, and a stop bit.

Given this general situation, I'm looking a explanation of how the Modbus protocol would function to obtain temperature data and control the relay.

[gmb42]

Have a look at this, explains all about Modbus protocol: https://modbus.org/docs/PI_MBUS_300.pdf

[WattsThat]

Here is an easy to digest example based set of explanations (I used this as a reference when writing my own arduino library just for the experience):

https://ipc2u.com/articles/knowledge-base/modbus-rtu-made-simple-with-detailed-descriptions-and-examples/