Specifications

Chapter 1 - Overview RS-422 And RS-485 Applications Ebook
Page 18 of 137 Manual Documentation Number: <DocNumber>
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Control of the RTS line must be set up in the communications software
controlling the serial port, to ensure that the RTS line is asserted
before data is applied to the TD line. The RTS line must be unasserted
(released) after the last data bit is sent. This not only decouples the
driver from the network, but also enables the receiver to accept
incoming data put on the communications line by other nodes on the
network.
RTS control is not usually suitable for Windows systems because RTS
timing cannot be closely controlled, which can result in lost data. For
additional details refer to RTS Control Timing Diagrams (on page 95).
If the RS-485 transceiver is connected to a two-wire multidrop
network, and if the RS-232 to RS-485 converter can be configured to
keep the receiver enabled all the time, the receiver will receive an
"echo" of the data transmitted by the driver. This is desirable in some
systems, and troublesome in others. Be sure to check the data sheet
for your converter to determine how the receiver "enable" function is
connected.
Send Data Control
Send Data control automates the process of enabling an RS-485
transceiver, removing the need to assert a hardware handshake line
each time data is transmitted. The RS-485 driver is enabled as soon as
data is detected at the input and disabled one character length after
the data stops.