20
7.3 RS-232 Connections
The following section describes the connection requirements for RS-232 cable. This cable will allow you to connect
the MJ-X
L
Control Panel to an RTU or personal computer.
Five of the standard RS-232 wires are used for this application.
•
Signal Return (RTN)
•
RXD
•
TXD
•
CTS
•
RTS
Table 7-2 lists the connections that must be made to connect the MJ-X
L
RS232/485 Communications Module to a
personal computer, RTU, or other supervisory device. The MJ-X
L
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.
Table 7-2 RS-232 Intelligent Electronic Device Wiring
MJ-X
L
RS-232/485
Communications Module
Personal computer, supervisory
device, or other network device
RTN
Signal Ground
RXD
TXD
TXD
RXD
Table 7-3 lists the connections that must be made to connect the MJ-X
L
RS232/485 Communications Module to a
modem.
Table 7-3 Modem Wiring
MJ-X
L
RS-232/485
Communications Module
Modem
RTN
Signal Return
RXD
RXD
TXD
TXD
RTS
RTS
CTS
CTS
“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.
