Day 3
Reinventing Modbus Protocol
Despite being a relic from the 70s, Modbus is still widely used in home and building automation applications due to its simplicity and interoperability. It is also extremely cheap to implement in hardware, making it a common choice for most related DIY projects. Unfortunately, due to its client-server architecture, the central controller of an installation must resort to polling to retrieve data and events from end devices. For some devices, like motion detectors or simple wall switches, this results in a significant delay between user input and the corresponding action. In short, Modbus installations can be terribly slow.

What we will demonstrate at the workshop is how to overcome this limitation of the protocol. This extension, known as 'fast Modbus,' employs clever tricks to achieve guaranteed 50ms latency while remaining completely compatible and relatively easy to implement. Bonus point: we can now scan the RS-485 line for devices in just a couple of seconds.

We will discuss the underlying theory of operation and then try it in action. We will observe the data on the RS-485 bus and attempt to send some bytes manually to achieve the same results.

The hardware aspect is quite straightforward, and we will primarily focus on bytes, so don't be scary of it.

Consider bringing your laptop.