TM

CONFIGURING A FIBER OPTIC

DATA TRANSMISSION LOOP

MARKET: Security,

Data, ITS

DOC. NUMBER: T-01

In many data transmission applications it is often

desirable to configure a loop, ring-type or drop-and-

repeat data bus in order to allow a “master” or host

controller to talk and/or listen to various local “slave”

units. When these units are located very far apart

from each other, or in an area that is prone to high

EMF levels or lightning strikes, a fiber optic trans-

mission system may be just the ticket. Such a sys-

tem will allow long distances to be traversed with no

concern as to noise pickup, ground loops or other

types of interference. CSI manufactures two fiber

optic data transmission systems that are ideal for

such applications: the FIBERLINK model 5012

Universal Data Transceiver and the FIBERLINK

model 5002 RS-232 Micro Transceiver.

by all local stations (including the master). In addi-

tion, any signal transmitted by a local station will also

ultimately return back to the master. The fact that

the original signal transmitted from the master is

ultimately received by the master allows the installer

to verify the overall integrity of the loop.

There are two basic requirements of such a sys-

tem. First, only one station may be permitted to trans-

mit data at any one time. Secondly, when not trans-

mitting data, the input to any transceiver must be in

the logic zero (or low) state. Since most master/

local systems employ this mode of operation, imple-

mentation is simple and straightforward.

In the drop-and-repeat configuration, all signals

transmitted by the master are received by all local

stations. Since the return fiber path is not used in this

configuration, the data is essentially transmitted in

one direction only

.

Both transceivers can be user-configured (by

means of integral DIP-type switches) and connected

to form a loop-type or a drop-and-repeat data bus

as shown in the diagram below. In the loop-type con-

figuration, any signal transmitted by the master con-

troller will be repeated around the loop and received

When configuring a data bus as described here,

be sure that your transceivers can accommodate

the data rate you plan to use. Also check that the

optical loss budget for the transceivers will not be

Fiberlink and TECHniques are trademarks of Communications Specialties, Inc.

© 1999, Communications Specialties, Inc.



Page 2: CONFIGURING A FIBER OPTIC DATA TRANSMISSION LOOP

exceeded. If you will be using Fiberlink Universal

Data Transceivers, all units within the loop will be

able to communicate with each other, even if set

for different protocols. When using Fiberlink

RS-232 Micro-Transceiver units, only RS-232 will be

supported.

When using a loop-type configuration, remember

that the transmitted signal will travel around the loop

and appear at the output of the master receiver port.

If desired, this output can be used to signify that the

loop is intact. If this feature is not needed, you should

configure the software to ignore the received “echo”.

Also, when using a loop-type configuration, it is

extremely important to set the fiber optic transceiver

connected to the master to “break” the loop (as

shown). Otherwise, a logic 1 signal could “lock up”

the loop and prevent further data transmission. When

using RS-485 two-wire protocol, it is also important

to set the “turn-around time” properly so that a com-

plete data word is transmitted before the transceiver

reverts to the high impedance receive state. The

Fiberlink Universal Data Transceiver provides a

wide range of user-selectable time intervals for just

this purpose.

•

Universal Data Transceiver ....................... 5012

•

Universal Data Trans. Card Version......... 5018

•

RS-232 Micro-Transceiver ........................ 5002

•

Educational Guide:

An Introduction to

Fiber Optics

•

Educational Guide:

An Introduction to Fiber

Optic Cable and Connectors

Fiberlink is a trademark of Communications Specialties, Inc.

© 1999, Communications Specialties, Inc.