Specifications

74 PCI-Comm Card Series User's Manual
RS-485 signal wiring
The RS-485 standard supports half-duplex communication. This
means that just two wires are needed to both transmit and receive
data. Handshaking signals (such as RTS, Request To Send) are
normally used to control the direction of the data flow and to switch
the transmission accordingly. In RS-485 mode, the PCI-1601/1602/
1612 automatically senses the direction of the data flow and switches
the transmission direction — no handshaking is necessary. This
means a user can build an RS-485 network with just two wires. This
RS-485 control is completely transparent to the user. The Software
written for half duplex RS-232 works without the need for any
modification.
RS-485 wiring topology
D.T.E
RS-485
Transceiver
D.T.E
RS-485
Transceiver
D.T.E
RS-485
Transceiver