Does anyone have any sample code or suggestions to help me to interface my 100 pin uc3a1512to a device via RS-485?
You need to put a RS-485 transceiver on your USART. Maybe a TI SN65HVD11, looks like it works with 3.3V IO.

As you you need to transmit, any sample that writes out the USART in asynchronous  mode will do.

As you don't mention having to share a RS-485 bus, tie the TX enable on on the transceiver.

That way RS-232 example code will work for you.