RS 485

Hi all!

I have a little problem. I have to make an RS 485 connection with an Arduino mega. Could you help me how can I get a Clear to Send (CTS) and a Ready To Send (RTS) signal from the panel? How can I write the program for it? It’s almost the same like the RS 232?

Thank you!

The RS485 standard does not use CTS/RTS. Those are RS232 signals.

More information would be helpful.

RS-485 does require a control signal:

“In contrast to EIA-422, which has a single driver circuit which cannot be switched off, EIA-485 drivers need to be put in transmit mode explicitly by asserting a signal to the driver. This allows EIA-485 to implement linear topologies using only two wires. The equipment located along a set of EIA-485 wires are interchangeably called nodes, stations and devices. [1]”

Here is post on the subject:


I have a circuit that allows you to skip the control pin by watching the data pin. This one is designed to connect to the PC

Thank you for the answers. Yeah, now I know that I don’t need the CTS, RTS signals. On the arduino board I have a 5 V signal, so I don’t have to convert the 12 V into 5 V from the PC RS-232 port. For the full-duplex connection, I guess I will need two SN75176 IC-s and some resisters. I almost know the connections but the thing what I don’t know is how to control the IC-s and the direction of the data flow.

You might want to check this: