Rs-232 Multi-Drop Wiring; Rs-232 Multi - Drop Configuration; Able 7-2 Rs-232 Intelligent Electronic Device Wiring; Table 7-3 Modem Wiring - Siemens MJ-4 Series Installation Manual

Table 7-2 lists the connections that must be made to connect the RS232/485 interface to a personal computer, RTU,
or other supervisory device. The MJ-4 Communications Module defaults to no-handshaking-required mode.
However, the communications module asserts RTS while it transmits data, but the module will ignore the CTS input
signal.
MJ-4 RS-232/485
Communications Interface
RTN
RXD
TXD
Table 7-3 lists the connections that must be made to connect the RS232/485 interface to a modem.
"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.

7.3.1 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.
RTU
Signal
Return
TX
RX
16
Table 7-2 RS-232 Intelligent Electronic Device Wiring

Table 7-3 Modem Wiring

MJ-4 RS-232/485
Communications Interface
RTN
RXD
TXD
RTS
CTS
Figure 7-6 RS-232 Multi-drop Configuration
Personal computer, supervisory
device, or other network device
Signal Ground
TXD
RXD
Modem
Signal Return
RXD
TXD
RTS
CTS
MJ-4
MJ-4
Signal Signal
Return Return
RX RX
TX TX
MJ-4
Signal
Return
RX
TX