Model 277 - Multimode Fiber Optic Modem



  • Point to Point or Ring Configuration
  • Data Interface Selectable RS-232, RS-422 or RS-485
  • Create a Ring of Up to 10 Units at 1 MBPS
  • Data Rate to 1 MBPS for RS-422 or RS-485
  • Use as Fiber Optic Line Extender
Telebyte, Inc. - RS-422, RS-232, RS-485

Product Description

The Model 277 is a unique asynchronous fiber optic modem whose optical interface can operate in either point to point or ring (daisy chain) configurations and whose electrical interface can also operate in point to point or multi-drop configurations depending on the user selected interface.

In an optical point to point configuration, two Model 277's are connected back to back to form a simple high speed, full duplex, optical link. In an optical ring configuration, two or more Model 277's are daisy chained in a ring. The ring will consist of a master Model 277 and one or more slave 277's. The slaves pass the received optical data along with the transmit data from their own electrical interface to their optical transmitters. The master does not pass the received optical data. Master/slave modes are switch selectable. A ring of up to 10 units at a data rate of 1 MBPS can be formed. To extend the optical distance between any two Model 277's another Model 277 can be inserted in the optical path to act as a line extender.

The Model 277 electrical interface is switch selectable between RS-232, RS-422 and RS-485. For RS-232, communications into the electrical interface is full duplex point to point. Data can be transmittedonto the optical fiber for a point to point optical link or for an optical ring. Switch selection enables data to flow from the electrical interface to the optical transmitter or to be controlled by the Request To Send, RTS, line.

Full duplex four wire, or half duplex, four or two wire may be selected when the RS- 422, RS-485 interface is selected. Your equipment with an RS-485 interface can be multi-dropped directly into the 277's interface. Operation in the RS-485 multi-drop requires that all devices connected to the line have some level of intelligence in order to establish an orderly flow of data. When the half duplex protocol is selected the Model 277 controls the transmit data line on the electrical interface. When no data is received by the optical receiver for 10 microseconds the output to the transmit data transceiver is placed in a high impedance state. In the 2 wire mode this enables many transceivers to communicate on the same twisted pair.

Model Description Product Info
277 Multimode Fiber Optic Modem
Specifications Manual Application Note
277-220 Multimode Fiber Optic Modem - 220 Volts
Specifications Manual Application Note

For more information, contact:
Phone: (727) 547-8307
Fax: (727) 547-0687


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