Model 276A



Reference Manual

0315-0306 Rev. B


Printed 02.04.02

Table of Contents

1.0 General Description
2.0 Specifications
3.0 Installation

3.1 RS-485
3.2 Fiber 3

4.0 Operation
5.0 Power
6.0 Help

1.0 General Description

The Model 276A Optoverter is a two-wire RS-485 to Fiber Optic Line Driver/Converter that can extend the distance of an RS-485 network to 6,600 ft. At the same time it provides the inherent advantages of transmission over fiber optic cable, immunity to interference, safety, secure communications, and more.


2.0 Specifications

Electrical: Half-duplex RS-485, two-wire

Fiber Interface: Optimized for 62.5/125 micron fiber cable

Wavelength: 850 nm

Speed: 0-1 MHz

Power Budget: 12 dB (with 62.5/125 micron fiber)

Distance: Fiber 2 km (distances can exceed 2 km depending on fiber loss)

RS-485: Per RS-485 specification

Connectors: Fiber (ST), RS-485 (DB-25 Female)

Power: 115 VAC/60 Hz (220 VAC/50 Hz optional)

Size: 3.5" L x 2" W x .875" H

Environment: 0 to 50 deg C, 5 to 95% RH (no condensation)


3.0 Installation

3.1 RS-485

The RS-485 connector to the Model 276A allows for half-duplex operation through a DB-25 female connector. Refer to the following chart for pin assignments.


Data Direction


Data I/O


Data I/O +


Signal Ground


3.2 Fiber

The fiber optic end has been optimized for operation with 62.5/125-micron cable and comes equipped with ST-type fiber optic connectors.

4.0 Operation

The Model 276A can be connected to any RS-485 device running at speeds up to 1 MHz. To connect the units, the connections "Data I/O-" and "Data I/O+" are connected to the two-wire data from the RS-485 equipment. Pin 7 is Logic Ground (if the customer's equipment requires it). To connect the 276A to another 276A, the fiber connector marked "T" should be connected to the far-end fiber connector marked "R" and the local "R" should be connected to the far-end "T."

5.0 Power

The Model 276A is powered by a small DC power adapter that supplies reduced DC voltage. In addition, power can be applied to the Model 276A by using Pin 9 on the DB-25 female connector and Pin 7 as the ground connection. When using this pin, the input voltage should be +12 VDC.


6.0 Help

If you require assistance, please visit our Technical Support Center.


TELEBYTE warrants the equipment to be free from defects in material and workmanship, under normal and proper use and in its unmodified condition, for 12 months, starting on the date it is delivered for use. TELEBYTE's sole obligation under this warranty shall be to furnish parts and labor for the repair or replacement of products found by TELEBYTE to be defective in material or workmanship during the warranty period. Warranty repairs will be performed at the point of manufacture. Equipment approved for return for warranty service shall be returned F.O.B. TELEBYTE factory and will be redelivered by TELEBYTE freight prepaid, except for non-continental U.S.A. locations. Non-continental deliveries will be sent COD freight plus import/export charges.

The above warranty is in lieu of all other warranties, expressed or implied, statutory or otherwise, including any implied warranty of merchantability or fitness for a particular purpose. TELEBYTE shall not be liable for any damages sustained by reseller or any other party arising from or relating to any equipment failure, including, but not limited to consequential damages nor shall TELEBYTE have any liability for delays in replacement or repair of equipment.

Out of warranty equipment may be returned to the Greenlawn, NY customer service facility prepaid as described above. Return shipping charges will be billed to the customer. The repaired unit will have a 90-day warranty. In those cases where "NO TROUBLE" is found, a reduced charge will be billed to cover handling, testing and packaging.

Whether in or out of warranty, a Return Material Authorization (RMA) number is necessary and can be obtained by visiting our Technical Support Center.  Reference the RMA number on the outside container.

Document No. 0315-0306/Rev. B


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