Specifications

Chapter 1 - Overview RS-422 And RS-485 Applications Ebook
Page 17 of 137 Manual Documentation Number: <DocNumber>
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third state to the driver output. Because of the three states (logic 0,
logic 1 and high impedance) the device output is called a tri-state
output. When in the high impedance state the output is sometimes
referred to as "tri-stated". In typical systems, control of the driver's
enable input is accomplished using RTS Control (on page 17) or Send
Data Control (on page 18).
RTS Control
One common application of RS-485 in a communication system is the
connection of several devices that have standard RS-232 serial
interfaces, to create a network. This typically requires conversion to
RS-485 using an RS-232 to RS-485 converter or an RS-485 serial card.
Figure 10: RTS Control
This may be implemented using the RTS control signal from an
asynchronous serial port to enable the RS-485 driver. The RTS line is
connected to the RS-485 driver enable such that setting the RTS line to
a high (logic 1) state enables the RS-485 driver. Setting the RTS line
low (logic 0) puts the driver output into the high impedance condition.
This in effect disconnects the driver from the bus, allowing other nodes
to transmit over the same wire pair.