Rs-232 Multi-Drop Wiring; Rs-232/485 Connections; Figure 5-7: Rs-232 Connector Pinout; Figure 5-8: Screw Terminal Connection - Siemens MJ-5 Installation Manual

"RXD" is an input for Data Terminal Equipment (DTE) and an output for Data Communications Equipment (DCE).
"TXD" is an output for the DTE and an input for the DCE. Personal computer serial ports are configured as DTE
and the modems are configured as DCE. The communications module RS-232 connections implement DTE.

5.3.1 RS-232 Multi-drop Wiring

Multi-drop configurations require that the respective pins of the DTE devices be connected in parallel, Figure 7-6.
The standard pin assignments for RS-232 connectors are shown in Figure 7-7.
Note: For Figure 7-6, the RTU port is wired as "DTE". When networking devices together, make sure the RTU
"data out" connects to the communications module Rxd, and the RTU "data in" connects to the communications
module Txd.
DE9
1 5
6
9

5.4 RS-232/485 Connections

The screw terminal block connector is keyed for proper insertion. Figure 7-8 shows the proper connector orientation.
Align the keys and insert the connector to interface to the RS-232/485 interface.
RTN
RXD
TXD
RTS
CTS
Figure 5-6 : RS-232 Multi-drop Configuration
Pin Signal
1 DCD
2 Rxd
3 Txd
DTR
4
Ground (Signal)
5
6 DSR
RTS
7
8 CTS
RI
9
* Shell (Frame Ground)

Figure 5-7: RS-232 Connector Pinout

Figure 5-8: Screw Terminal Connection

MJ-5 Communications Module
Signal Return
RXD
TXD
RTS
CTS
DB25
1 13
14 25
* For Shielded Cable Connectors
Pin Signal
1 Ground (Frame)
2 Txd
3 Rxd
RTS
4
5 CTS
6 DSR
7 Ground (Signal)
8 DCD
DTR
20
22 RI
* Shell (Frame Ground)
9