You need to do a bit more research to properly define your question. RS484 is non existent, you probably want RS485. The ASCII protocol is a query-response or a question and answer communication protocol in which a host PC uses ASCII characters to send commands to a device and then receives responses back from that device. ASCII is abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Most modern character-encoding schemes are based on ASCII, although they support many additional characters. Modbus RTU is an open, serial (RS-232 or RS-485) protocol derived from the Master/Slave architecture. It is a widely accepted protocol due to its ease of use and reliability. Modbus RTU is widely used within Building Management Systems (BMS) and Industrial Automation Systems (IAS). There are a lot of libraries available. You need to do more work so you understand what you are trying to ask. I would suggest you start by getting the Arduino cookbook and reading it. Also on line there are many videos etc showing the Arduino and how to do what you want. This will do a lot to help you. Also if you go to the Gigs and Collaborations if you want somebody to write the code for you.