My multifunction meter only have rs485 communication port but I have never worked with rs485 using 8051 microcontroller. Can someone guide me how to realize the same? The main function is to transfer a value from meter to controller.
The instrument doesn't care that you have a 8051 chip.
So work with TIA-485 (or read Google information) just as if you used a different processor.
And figure out if you would use two-wire or four-wire communication.
And figure out how/when to turn off the driver circuit.
And figure out how to handle termination.