You should get exactly the same data back in to the receiver, as you send it. Send the data as a continuous burst, then set the control output low again. To transmit, wait for at least one character period with nothing received then set the control output high to enable the driver.
![codevision avr usart example codevision avr usart example](https://softsoldier.com/wp-content/uploads/2019/09/CodeVisionAVR-Advanced-3.14-For-Windows-102.jpg)
The default state is then that the signal from the balanced line bus is passed to the receive input of the MCU UART. Just connect TXD to DI, RXD to RO, /RE to ground and another output pin on the MCU to DE. They differ about power consumption and maximum transfer rate. There are many usable chips for using as RS485 transceiver. Here an example of microcontroller connection.
![codevision avr usart example codevision avr usart example](https://static.cdn.asset.aparat.com/avt/7190635-5776__8275.jpg)
You can use isolated RS485 Transceivers or use a own circuit to do this. Normally there is no isolation between the bus subscribers. Your schematic looks like a isolated detection for a -24V signal. I would switch the LED on when one proper frame was received, and switched off after a short period of 40 to 100ms. When less data on the signal in port the LED flickers so short, that no light can bee seen. The LED can be switched on and off by an dedicated port of Your microcontroller, when receiving some proper signal by USART. When want to use only 2 wires the system only can work in half duplex mode and transmitter had to be switched off while receiving. When using a 4 wire RS485 Connection the transmitter and receiver of the RS485 Chip can be enabled fix. Normally for the transmisson You can use the USART of Your microcontroller.