Specifications

Chapter 1 - Overview RS-422 And RS-485 Applications Ebook
Page 13 of 137 Manual Documentation Number: <DocNumber>
www.bb-elec.com/
www.bb-europe.com/
Note: If all RS-485 drivers on a communications line are tri-stated (high impedance), the outputs
are floating and will not measure the voltage shown.
Balanced differential line receivers sense the voltage state of the
transmission line across the two signal input lines, A (-) and B (+).
When V
AB
is between -200 mV and -6 volts the receiver interprets the
signal as a logic 1 or mark. When V
AB
is between +200 mV and +6 volts
the receiver interprets the signal as a logic 0 or space.
RS-422 and RS-485 Terminals and Designations
There are a number of different RS-485 devices used in RS-485
communications systems. Some have their transmitter and receiver
data lines available separately, enabling them to be used in RS-422 or
RS-485 four-wire systems. Others internally bridge the driver and
receiver data lines so that they can only be used in two-wire mode. Still
others can be user-configured for two- or four-wire operation using
switches, jumpers or external wiring.
Figure 6: RS-485 Chip with TD and RD pins available