Transmission Methods; Fiber Optic Transmission; Wire Transmission; Figure 2-1 Fiber Optic Network - Siemens MJ-XL Installation Manual

• Watchdog when blinking steadily, indicates the MJ-X
are functioning properly.
• Communications indicates communications activity with this module. (The Comm Module turns on this
indicator when it receives a valid message with a valid address.)
• Rxd indicates the communications module is receiving data.
• Txd indicates the communications module is transmitting data.

2 Transmission Methods

There are two transmission mediums available for sending data to the RTU:
• fiber optic
• wire

2.1 Fiber Optic Transmission

The primary benefits of fiber optic communications are its immunity to induced electrical interference and
relatively low signal loss. Electrical noise cannot be induced into the cable to generate transient spikes that disrupt
data communications.
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The MJ-X Fiber Optic Communications Module uses multi-mode fiber optic cable. The electrical signals are
converted to optical signals by the communication unit. The optical signals are then transmitted via the fiber optic
cable to the RTU. Communications modules in the path between the transmitting communications module and the
RTU act as repeaters and simply regenerate the signals and forward them to the next device, Figure 2-1.
Out
RTU
In

2.2 Wire Transmission

The advantage of wire transmission is simple installation. The MJ-X
232 and RS-485. The screw terminal block connector supplied with the module can be wired for either interface.
Connection to the supervisory device is typically accomplished using either a DE-9 or DB-25 connector for RS-
232, while the connector used for RS-485 will vary with the application.
2.2.1 RS-232
Direct RS-232 connections are limited to a maximum distance of 50 feet, Figure 2-2. The MJ-X
Communications Module supports RS-232 multi-drop configurations.
2
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Communications Module microprocessor and software
MJ-X
In Out
Fiber Optic Cables

Figure 2-1 Fiber Optic Network

MJ-X
In Out
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supports two popular wire interfaces: RS-
MJ-X
In Out
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RS-232/485