National Instruments NI 9871, RS422, RS485 RS485 Bus Topology and Termination

© National Instruments Corp. 11 NI 9871 Operating Instructions
RS485 Bus Topology and Termination
Refer to Figure4 and Figure 5 for an overview of 4-wire and
2-wire RS485 bus topologies and termination.
Figure 4. 4-Wire Full-Duplex Multidrop Network Using Terminating Resistors
Figure 5. 2-Wire Multidrop Network Using Terminating Resistors
RS485 terminators are available at ni.com/serial.
MASTER
Slave 1
120 Ω
Slave 2 Slave n
120 Ω
Tx
Tx Rx Tx Rx Tx Rx
Rx 120 Ω120 Ω
MASTER
Slave 1
120 Ω
Slave 2 Slave n
120 Ω
Tx
Tx Rx Tx Rx Tx Rx
Rx