Rockwell Automation 2755 Enhanced Decoder Series B - Manual (Page 324)

Connecting to a Host E–6
Publication 2755-833
The RS-422 interface uses pins D, P, R, S, T, U, and V of the HOST
port connector. The transmit data and receive data lines are:
Pin P TxB+ Transmits data from the decoder to the host.
Pin R TxA– Transmits data from the decoder to the host.
Pin S RxA’– Receives data from the host.
Pin T RxB’+ Receives data from the host.
RS-422 communication lines are unterminated. To enable network
termination (120 Ohm resistor in series with a 0.01 microfarad
capacitor), connect pins U and V together.
Important: We recommend you terminate the RS-422 lines if
excessive noise occurs on long RS-422 communication links.
RS-422 does not use modem control lines. However, the
configuration software does allow optional flow control using
XON/XOFF characters. The options are:
•
RS422. No flow control.
•
RS422 XON/XOFF. Enable XON/XOFF flow control.
The RS-422 communication interface and protocol is selected during
configuration. See the Host Communications configuration screen.
The DH485 interface allows you to multi-drop up to 31 decoders to
each port of the Flexible Interface Module (Catalog No. 2760-RB).
Each of the three ports of the module operates as a separate
communications network.
Figure E.5 shows how to connect the NEMA Type 1 decoder to a
DH485 network. Use Belden cable 9842 (or equivalent).
RS-485 Using
DH485 Protocol