Modbus communication?

Hello all, I need to get temperature data from control temperature and I have problem How to use arduino communicate with Temperature control (dixell XR20CX) by Modbus interface

[u]Communication detail[/u]

modbus RS485 RS232 control temp -----------------> XJ485-CX ----------------> Interface to RS232 ------------> Arduino (dixell XR20CX)

Information 1. dixell XR20CX use Modbus RTU 2. I can use dixell XR20CX interface to PC by Modbus32 software and got temperature Device ID :1 Address: 257 Range:1 type Holding Register (type I'm not sure) RS232 baudrate 9600 Length 8 Parity NONE Stop bit: 1

  1. I think should use example from I need help modify code for get data address 257 rage1 only

Thank you.