Overview

The objective of this project is to control the Jandy heater using the RS485 interface.

Model: Jandy JXi Gas-Fired Pool and Spa Heater 260N

RS-4865 Interface

RS485 protocol, wiring & adapters

All pool equipment uses a half duplex RS485 protocol to comunicate between Control Panel, Keypads and inteligent Devices like Salt Water Generators, Variable Speed Pumps, Chemical feeders & some heaters.

There are a few main problems areas that you should have a basic understanding of, that can effect the performance.

• RS485 Wiring and Termination (The majority of issues new people have are here)

• RS485 USB Adapters and how they actually work in reguard to Pool equiptment. (this becomes very important on busy RS485 bus)

Wiring and Termination

Below is a basic diagram of an RS485 bus

As you can see, each device is connected to 3 wires (Data+, Data- & Ground), and there is a termination resistor at each end of the wiring (or bus).
The ground connection is their so the adapter has a referance point for the voltages in Data+ & Data-, and there is some level of circuit protection.
The termination resistors are their to prodide clear signals and stop reflection. Here is a detailed article on that

References