Data Flow Control - Advantech ADAM 4000 Series User Manual

RS-485 Network
E.3 RS-485 Data Flow Control
The RS-485 standard uses a single pair of wires to send and receive data.
This line sharing requires some method to control the direction of the data
flow. RTS (Request To Sent) and CTS (Clear To Sent) are the most
commonly used method.
Intelligent RS-485 Control
ADAM-4510 and ADAM-4520 are both equipped with an I/O circuit
which can automatically sense the direction of the data flow. No handshak-
ing with the host (like RTS, Request to Send) is necessary to receive data
and forward it in the correct direction. You can use any software written
for half-duplex RS-232 with an ADAM network without modification.
The RS-485 control is completely transparent to the user.
E-8 ADAM 4000 Series User's Manual
Figure E-6 RS-485 data flow control with RTS