Interface Home Assistant and MODBUS HMI

I’m planning to replace and ancient Heating system with Home Assitant. This system has many temperature sensors, some relais cards and some LCD HMI. All connected with RS485 and MODBUS RTU protocol. No problems with sensors and relais, but I don’t know how configure the HMI. HMI is a modbus slave. Original controller read temperature setpoint for each HMI and write temperature of each room. When a setpoint is changed the controller write new preset to each hmi. Every HMI can control all the rooms, every room has a different holding registry for setpoint and one for temperature.

Someone have any ideas?