How to integrate,monitor and control home alarm system using RS485 - TCP/IP?
Rs485 is generally a 1 wire protocol. The key feature is that it uses the parity bit to indicate an address byte at the start of the message. 

A similar device made by honeywell I've been looking at uses 1200 baud 8 bit 1 stop bit parity 1 on address bytes and 0 otherwise. The wire is pulled up to 5 v and is pulled low by whatever device wants to transmit. 

Standard os serial drivers won't let you set the parity bit at will so I had to use a separate uart along with a bit of circuitry to drive the line properly and some python code to drive the uart off a raspberry pi's i2c bus.

Then of course you have to decode the actual messages sent over the serial connection.