The RS-485 is the electric standard used for assyncronous serial data transmission, therefore there is no impediment to you make simulations with e.g a generic UART acting as the Master device. I have used the VSPE serial port emulator for this purpose with Proteus.
what i need is an example for converting from rs232 (pc) to rs485 connected with avr microcntroller
i had tried a lot of circuits in the internet and it doesn't work