I am using Docklight software in windows to read data from rs485 to usb converter .i am correctly getting data .but in linux I am not able to receive response data when i Transmit data.Tried with minicom software in linux.it shows ftdi driver for rs485 to usb converter .
Software drivers don't know if there is RS232 or RS485 connected. The serialisation and deserialisation process is the same.
But there are some differences with the control lines. For RS485 you need a "driver enable" signal. To transmit data.
If you use the RS485 true half duplex (only one pair of signal lines) then you need to disable the driver during receive to avoid short circuit.
Recent FTDI chips, e.g. FT232R have a hardware TX-Enable signal that is set in the configuration EEPROM. It's enabled in the default configuration, a RS485 driver connected according to FTDI example circuit will work without a specific RS485 driver.
It depends. FTDI USB-to-UART bridges can generate it automatically, review the datasheet. Also some µC UARTs can provide a hardware generated enable signal, e.g. PIC24. Otherwise it must be software generated.