Serial Data Communications Over Fiber Optic Cable

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Figure 5-11: The Model 9271 Fiber Optic Auto Powered Line Driver features a standard DB9 interface

The Model 9271's ability to take/direct data from/to this interface without any conversion eases

implementation. A highly flexible solution, the Model 9271 has been optimized for 62/125 fiber cables,

and is compatible with other sizes as well. It features industry-standard ST cable port connectors, plus a

DTE/DCE switch to reverse Pins 2 and 3 of the RS-232 connector to accommodate equipment with

different data output configurations.

Operating current for the Model 9271 is derived from the transmit data line, with a power budget of 12

dB when using 62/125 cable. For applications requiring a dedicated power source, the unit can be

ordered with a wall-mounted power pack (available as the Model 9271A).

The Model 9271 incorporates clips in the outer casing so that the unit can be securely attached to a DIN

rail, wall, table or desk in an organized manner.

This is an appropriate point to discuss DIN Rail mounting in greater detail. DIN Rail mounting is a

cabling system that was developed specifically for factory automation. Only recently has it been

discovered for use with data equipment. This system is simple and straightforward. It uses a steel

channel called a DIN Rail. The DIN Rail has slotted holes for mounting and is normally mounted in a

horizontal position. DIN Rail products like the Model 9271 are then placed on the Rail by snapping

them in place after which the wiring is completed.

CHAPTER 6

SERIAL DATA COMMUNICATIONS OVER FIBER OPTIC CABLE

In the premises environment the most common form is serial data communications. This is the situation

where data embarks from the Source at a serial interface and enters the User at a serial interface. Serial

data communications is everywhere in the office, campus or industrial environment. It is found, on the

factory floor, in the hospital, in the retail establishment and out in the oil patch. This list goes on and on.

In this chapter we consider premises serial data communications carried out using fiber optic data links.

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Products are introduced that support this type of communications. Some of these products have been

introduced in previous chapters. Others are new. All of these products are available from Telebyte.

Model 271 Fiber Optic Auto Powered Line Driver

The Model 271 Fiber Optic Auto Powered Line Driver is pictured as a stand-alone unit in Figure 6-1.

Figure 6-1: Model 271 - Fiber Optic Auto Powered Line Driver

The Model 271 Fiber Optic Auto Powered Line Driver is a short haul modem that employs an RS-232

data interface and transmits the data on a fiber optic cable. This modem provides, full duplex,

asynchronous, data communications over two fiber optic cables. The length of the fiber optic cable can

be up to 2 km and the data rate as high as 56 KBPS. Performance of the unit is optimized for 62.5/125-

fiber optic cable. However, the modem can also be used with fiber optic cable having other dimensions.

The operating power for the Model 271 Fiber Optic Auto Powered Line Driver is derived from the

transmit data line. This is a real convenience when an electrical outlet is not readily available. The

Model 271 is equipped with a DTE/DCE switch that reverses pins 2 and 3 of the RS-232 connector. This

allows the modem to support terminals, printers, computers or any other RS-232 based device. The fiber

port of the unit employs ST connectors.

One application of the Model 271 is illustrated in Figure 6-2. Notice while this application deals with the

factory environment there is no card cage. Rather, the application is dealing with the situation where

there is the need for a data communication link between a mini-computer located in the front office of a

company and a PC located on the company's factory floor. Both the front office and the factory floor are

in the same building.

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Figure 6-2: Example Application of the Model 271

Data communication carried out strictly in the front office may be quite reliable over copper cable.

However, because the data communication link in this application traverses the boundary to the factory

floor there is a need for the extra reliability provided by fiber optic cable.

Model 274 RS-232 Single Fiber, Sync/Async Line Driver

The Model 274 RS-232 Single Fiber, Sync/Async Line Driver is pictured as a stand-alone unit in Figure

6-3.

Figure 6-3: Model 274 - RS-232 Single Fiber, Sync/Async Line Driver

The Model 274 is a unique short haul modem for use on a fiber optic data link. To achieve full duplex

communication it only requires one multi-mode 62.5/125-fiber optic cable. Most fiber optic data

communication networks require two cables to achieve full duplex operation. In fact, if standard duplex

fiber optic cables have been installed the Model 274 can be used to double the capacity.

The Model 274 receives and delivers data through an RS-232 interface. This unit supports nine

synchronous data rates up to a maximum of 256 KBPS. It supports asynchronous data rates up to 38.4

KBPS. Furthermore, it supports two pairs of handshake control signals, RTS/CTS and DTR/DSR.

The Model 274 has operator selectable, built-in diagnostics. These include Local Loop-back and Remote

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Loop-back.

The data interface to the modem is a female DB25 connector. The fiber port interface is a ST connector.

LED's for TD, RD, control signals and loop-backs allow the unit to assist in verifying link operation.

The four illustrations in Figure 6-4 indicate how the Model 274 may be employed in typical

applications.

Figure 6-4: The Model 274 employed in typical applications

Model 279 Multi-Mode to Single-Mode Fiber Optic Converter

The Model 279 Multi-Mode to Single-Mode Fiber Optic Converter provides such conversion. It is

pictured in Figure 6-5.

The Model 279 Multi-Mode to Single-Mode Fiber Optic Converter provides transparent conversion

between multi-mode fiber optic cable signals and single-mode fiber optic cable signals. As alluded to

above single-mode fiber optic cable can transmit data over much longer distances than multi-mode fiber

optic cable. Single-mode operation is at a 1310 nm wavelength. Multi-mode operation is at 850 nm

wavelength.

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Figure 6-5: Model 279 - Multi-Mode to Single-Mode Fiber Optic Converter

There are many applications for the Model 279. This unit can be employed as an individual converter. A

pair of these units can also be employed as single-mode, fiber optic cable, and short haul modems in

order to signal over long link distances. The unit can also be used when the optical fiber type of the

equipment is not compatible with the installed type of fiber optic cable e.g., you have a modem

transmitting multi-mode signals but the installed fiber optic cable is single-mode.

The Model 279 operates at speeds from DC to 2.5 MBPS over links that can be as much as 15 km long.

Since operation at DC is possible there is no signal that can be used to perform automatic gain control.

However, the unit allows the needed control, to be executed manually, by a Line Loss Switch.

The Model 279 is illustrated in one of many possible applications in Figure 6-6. This is an application in

an industrial environment. There are two manufacturing facilities in the company associated with this

application. These two facilities are remotely located from one another. They are 15 km apart. The

process control computer located on the floor of one facility needs to communicate with the local

controller in the other facility. Both the process control computer and the local controller employ the

RS-422 interface. As shown in Figure 6-8 both the process control computer and the local controller

have data converted to fiber optic signals using the Telebyte Model 272A. However, these signals are

multi-mode. In order to cover the large 15 km distance between the two facilities single-mode fiber optic

cable must be employed. Placing a Model 279 at the fiber output of each Model 272A allows the

conversion to the needed single-mode signals.

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