Using RS-422 and RS-485 Devices
19
GND
GND
TXA TXB RXA RXB
RS-485
MASTER
TXA TXB RXA RXB
RS-485
TXA TXB RXA RXB
RS-485
GND
GND
SLAVE
SLAVE
Figure 3-2: Two-wire RS-485 System
In the two-wire system diagrammed in Figure 3-2, one pair of transmit and receive lines
(TXA and RXA) are connected to a single wire and the other pair of transmit and receive
lines (TXB and RXB) are connected to the second wire. The device that is designated as the
master manages the traffic on the lines.
As shown in the above diagram, the pair of transmit/receive lines needs to be terminated
with 120 ohms at each end of the bus.
