1.0 Equipment Description

1.1 General
The Model 2277, Multimode Fiber Optic Modem, is an asynchronous fiber optic modem. The optical interface can operate in either point-to-point or ring configurations. The interface employs two "ST" type connections. The unit operates on fiber optic cables with core diameters from 50 to 100 microns. The model 2277 is fully compatible with Telebyte's non rack models 277 and 8277.

The electrical interface operates in either point-to-point or multidrop configurations. When configured as RS-232 or RS-422 the unit will operate point-to-point. With the RS-485 interface selected, equipment can be multidrop connected, onto low cost twisted pair, 2 and 4 wire. See Figure 1. This interface can be connected directly to the customers equipment or to a Telebyte Model 285 Superverter™. The versatility of the two interfaces of the Model 2277 allows for extremely flexible system design.

Figure 1 - RS-485 Multidrop Configuration
1.2 Optical Interface
In an optical point-to-point configuration, two Model 2277's are connected back to back to form a simple high speed full duplex optical link. In optical ring operation, 2 or more 2277's are cascaded in a ring. A ring consists of one master modem and 2 or more slaves. See Figure 2. The slaves pass the received optical data, along with the transmit data from their electrical interface, to their optical transmitters. The master does not pass the received optical data. Master/slave modes are switch selectable. Master mode is selected for both modems in an optical point-to-point configuration.

Figure 2 - Optical Ring
The Model 2277 optical interface can form a ring of up to 10 units. This allows for a maximum optical system loss budget of 120 dB. In order to extend the optical distance between any two Model 2277's, Model 2277's can be inserted in the optical path to act as line extenders. Slave mode should be selected for optical line extenders. See Figure 3.

Figure 3
Note:
The Model 2277 uses infrared light for communications. This is not visible to the eye.
2 wire Rs485 will not work in a ring configuration with TD control.

1.3 Electrical Interface
The Model 2277's electrical interface is switch selectable to RS-232 or RS-422/RS-485 voltage levels. When the RS-232 interface is selected, communications to the electrical interface is full duplex, point to point. With this interface, data can be transmitted onto 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 can be controlled by a high on RTS. On the electrical interface, a high on the data in pin causes light to be emitted.

Full duplex (4 wire) or half duplex (4 or 2 wire) may be selected when the RS-422/RS-485 interface is selected. The RS-422/RS-485 interface of the Model 2277 may operate in a multidropped or point-to-point environment. If RS-422 is selected the electrical interface is point-to-point only. If the customer's equipment has an RS-485 interface it can be multi-dropped directly onto the Model 2277's interface by selecting the 4 wire or 2 wire RS-485 mode. If the customer's equipment has an RS-232 interface a Telebyte Model 285 can convert the equipment to a multidrop, RS-485 interface. Up to 31 units of the Model 285 can be multidropped onto the same electrical interface of the Model 2277. The pinout of the RS-422 or 4 wire RS-485 electrical interface conforms to EIA-530.

1.4 Flow Control
Operation in the RS-485 multidrop or the ring environment requires that all devices connected to the line have some level of intelligence, in order to establish an orderly flow of data. When RS-485 (half duplex) is selected the Model 2277 controls the Receive Data line on the electrical interface. When no data (no light on fiber) is received by the optical receiver for 10 microseconds the output of the Receive Data electrical transmitter is tri-stated. In the RS-485 mode this enables many transceivers to communicate on the same twisted pair. When the RS-485 2-wire mode is selected, half duplex data is transmitted and received on the same twisted pair.

2.0 Specifications

2.1 Optical Interface
Optical connectors - ST™ (trademark AT & T.)
Power Out - > +15 dBuW (32 microWatts), into 62.5/125 um core/clad fiber.

Power Budget - > 12 dB - on 62.5/125 um core/clad fiber
Wavelength - 850 nm, multi-mode
Optical Configuration - Switch selectable, Master/Slave

2.2 Electrical Interface
Electrical connector - DB-25, male
Interface type - Switch selectable -

RS-232 (pinout conforms to RS-232)
RS-422, or RS-485 (4 wire pinout conforms to EIA-530)

Bit Rate -

RS-232 - 0 to 115.2 KBPS
RS-4XX - 0 to 1 MBPS

Interface Mode - Switch selectable - Unit can be configured to appear as a DCE or a DTE
Power connections - Card Edge

The Telebyte Model 2200 Rack powers the unit.
The unit is provided with a HOT SWAP circuit allowing the unit to be removed and replaced in the Rack with power applied.

2.3 General Specifications
Indicators - 4 LED's -

LTD - Local Transmit Data
FTD - Fiber Transmit Data
RD - Receive Data
FULLDUX - Full Duplex

Environment - 0° to 50° Celsius, 5% to 95% RH non-condensing.
Size - .8" W x 10.25" L x 6.3" H

3.0 Equipment Operation

3.1 Switch Options
The Model 2777 is a very versatile piece of equipment. It has many switch selectable options than can be used to tailor it to the user's communications requirements. The following tables list the switch selections and their functions.

Front Panel Switch Option

Bottom Dip Switches

3.2 Connections
After the switches have been set up properly, the connections to the Model 2277 I/O ports must be made. There are 3 groups of connections. These are the fiber optic interface, the electrical interface, and the power interface. A minimum of two Model 2277's are required for communications.

The connections to the fibers are through two ST connectors on the front of the Model 2277. These are marked T for optical transmit and R for optical receive. The fibers, between the two communicating Model 2277's, must be cross connected. That is to say that the optical transmitters must be connected to the optical receivers. The Model 2277's optical power budget is specified as 12 dB, using 62/5 um core fiber. These units may use fibers with other core diameters. The table below specifies the loss budget for the different fibers.

Max. Optical Loss Budget
The connections to the electrical interface are through the DB-25 connector located on the rear of the Model 2277. The signals on these pins are shown in the tables below. These signals and their functions and directions vary with the switch settings. The minimum requirement for proper connection is for a TD, RD and GND. The tables below show the signal names and their sources for the various settings of the DCE/DTE switch and the 232/4XX switch.

The Model 2277 is powered from the Model 2200 Fiber Optic Card Cage.

Electrical Interface Pinouts
RS-232, Switch in DCE position

RS-232, Switch in DTE position

RS-422/RS-485, 4 wire, Switch in DCE position

RS-422/RS-485, 4 wire, Switch in DTE position

RS-485, 2 wire, Switch in DCE position

RS-485, 2 wire, Switch in DTE position

Note: When connecting to the Telebyte, Model 285, polarities of the TD and RD pins must be reversed.

4.0 Indicators

On the front panel of the Model 2277 are four LED indicators. These indicators can be used to see the status of the Model 2277 and the user's equipment. Below is a list of the LED's and their functions.

Ext. Alarm Output - The model 2277 is supplied with a internal power monitor that will light up the external alarm indicator on the model 2200 Card Cage Power Supply if the model 2277's onboard power supply falls.

LTD - Local Transmit Data - This LED is used to monitor the data coming into the electrical interface from the user's equipment. For RS-232, a positive voltage on the data entering the Model 2277 turns this LED on when either one of the following conditions is met: a) with the DCE/DTE switch in the DCE position pin 2, TD will turn on the LED or b) with the switch in the DTE position pin 3, RD will turn on the LED.

For RS-4XX, and the DCE/DTE switch in the DCE position, a voltage more positive on pin 2, TD+, than on pin 14, TD-, turns this LED on. With the switch in the DTE position the lines monitor are pin 3, RD+, and pin 16, RD-.

Note: In RS-485 2-wire mode when configuring the Model 2277 in an optical ring, the master cannot be enabled by the "TD" signal, it must use RTS/CTS to control transmitter.

FTD - Fiber Transmit Data - This LED turns on when light is transmitted from the optical transmitter. In the slave mode this is the logical "OR" of light coming into the optical receiver, and a high on the data coming from the user at the electrical interface (LTD.) In the master mode this is the same as LTD.

FRD - Fiber Receive Data - This LED is used to monitor the data into the optical receiver. The LED turns on when there is light on the fiber connected to the receiver.

FULLDUX-Full Duplex - This LED is used to monitor collisions on the fiber. This indicates a system problem. This LED turns on when the Model 2277 is being used in an optical ring and more than one slave is trying to transmit to the master unit. In the master mode this LED is disabled.

5.0 Help

If any assistance is required call Bomara Associates at (800)-5BOMARA or (978)-452-2299.
Technical Support E-Mail: bobr@bomara.com
or use our Online Contact Form

Document No. 0315-0307
Rev -

Warranty

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. These deliveries will be sent COD freight and 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.