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Model 274 - Single Fiber, Sync/Async
Short Haul Modem Reference Manual
1.0 Description
The Model 274 Si-Fi™, Single Fiber, Fiber Optic Modem/Line Driver,
allows either asynchronous or synchronous devices to communicate over
a single fiber. The Model 274 transmits full duplex data at speeds upto
256 KBPS sync, or 38.4 KBPS async, and two full duplex control signals
over distances of 2.5 km. The Model 274 can also be configured to operate
to distances of 5 km but with a reduction in the speed to 64 KBPS sync
or 19.2 KBPS async.
Communication between the Model 274's is accomplished using a 3B4B encoding
method. The encoding and decoding are transparent to the user.
2.0 Specifications
2.1 Interface : RS-232 - conforms to EIA-232
Fiber - Multimode 62.5/125 um
2.2 Connectors : RS-232 - DB-25F
Fiber - ST connector
2.3 Speed
Standard Mode
Synchronous - 2.4, 9.6, 19.2, 38.4, 48, 56, 64, 192, and 256 KBPS
Asynchronous - DC to 38.4 KBPS
Extended Distance Mode
Synchronous - 9.6, 19.2, 38.4, 48, and 64 KBPS
Asynchronous - DC to 19.2 KBPS
2.4 Indicators : TD, RD, DCD, Link (indicates when units are linked),
LOCAL LOOPBACK *, and REMOTE LOOPBACK *
*Note - Local and Remote LED's only indicate when the individual switch
has been depressed.
2.5 Switches : 12 Position DIP Switch - sets speed, handshake mode,
and clock mode; Local Loopback; Remote Loopback
2.6 Size : 5"W x 1.5"H x 5.3"D
2.7 Distance
2.5 km Standard Mode
5 km Extended Distance Mode
2.8 Power Budget : 14 dB
2.9 Wavelength : 850 nanometer, multimode
2.10 Power : 115 VAC 60 Hz (220 VAC 50 Hz optional)
3.0 Installation
3.1 Digital Interface
The digital interface to the Model 274 is a DB-25 female connector that
is configured as a DCE device. The following signals are supported:
| Pin |
EIA |
CCITT |
Name |
Direction |
| 1 |
101 |
AA |
FG |
Chassis GND |
| 2 |
103 |
BA |
TD |
Input |
| 3 |
104 |
BB |
RD |
Output |
| 4 |
105 |
CA |
RTS |
Input |
| 5 |
106 |
CB |
CTS |
Output |
| 6 |
107 |
CC |
DSR |
Output |
| 7 |
102 |
AB |
GND |
Signal GND |
| 8 |
109 |
CF |
DCD |
Output |
| 15 |
114 |
DB |
TC |
Output |
| 17 |
115 |
DD |
RC |
Output |
| 20 |
108.2 |
CD |
DTR |
Input |
| 24 |
113 |
DA |
ExCLK |
Input |
3.2 Fiber Optic Interface
Connection between a pair of Model 274's is accomplished through a single
fiber optic cable. This cable is connected to the female ST connector
located on the rear of the Model 274. The connector comes equipped with
a removable plastic caps that is used to protect the fiber optic component
from contamination. To connect two Model 274's together, connect a single
fiber optic cable to the connector marked Fiber on both units.
4.0 Operation
The Model 274 has a number of user configurable options that can be changed
by way of a 12 position dip switch located on the bottom of the unit.
Options include speed setting, selecting a clock source and handshake
modes. Besides the user options the unit can be placed in one of two loopback
modes, local and remote, by pressing one of front panel switches.
4.1 Speed Setting
The Model 274 can be configured to operate in one of two modes standard
or extended distance. In the standard mode the user can select one of
nine data rates up to a maximum of 256 KBPS. The extended distance mode
is used when longer distance links are required. Typically the unit will
work with up to 14 dB loss or over distances of 2 km. The unit will not
operate beyond 2 km due to timing considerations caused by delays over
the fiber. To go farther than 2 km the unit can be configured to operate
in the extended distance mode whereby the maximum speed is reduced to
a rate 64 KBPS. Configuring the unit for Extended Distance mode does not
increase the loss of the unit,it is constant at 14 dB. See the accompanying
chart for the different speed settings.
Standard Mode
Switch
4 |
Position
3 |
Synchronous
2 |
Mode
1 |
Speed |
| 0 |
1 |
1 |
1 |
2.4 |
| 0 |
1 |
1 |
0 |
9.6 |
| 0 |
1 |
0 |
1 |
19.2 |
| 0 |
1 |
0 |
0 |
38.4 |
| 0 |
0 |
1 |
1 |
48 |
| 0 |
0 |
1 |
0 |
56 |
| 0 |
0 |
0 |
0 |
64 |
| 1 |
0 |
1 |
0 |
192 |
| 1 |
1 |
1 |
1 |
256 |
Standard Mode
Switch
4 |
Position
3 |
Asynchronous
2 |
Mode
1 |
Speed |
| 0 |
0 |
0 |
1 |
DC to 38.4 |
| 0=Off |
|
1=On |
Extended Distance Mode (Sync Mode)
Switch
4 |
Position
3 |
Synchronous
2 |
Mode
1 |
Speed |
| 1 |
1 |
1 |
0 |
9.6 |
| 1 |
1 |
0 |
1 |
19.2 |
| 1 |
1 |
0 |
0 |
38.4 |
| 1 |
0 |
1 |
1 |
48 |
| 1 |
0 |
0 |
0 |
64 |
Extended Distance Mode (Async Mode)
Switch
4 |
Position
3 |
Asynchronous
2 |
Mode
1 |
Speed |
| 1 |
0 |
0 |
1 |
DC to 19.2 |
| 0=Off |
|
1=On |
4.2 Selecting A Clock Source
The Model 274 can operate using internal or externally generated clock
signals. The unit provides transmit and receive clock on pins 15 and 17
and accept a clock on pin 24.
The diagram and chart shown below, describe a configuration of two modems,
a computer and a terminal. The clocking options refer to the sources of
the system clock. There are three sources of the clock. A system clock
can be internally generated by either modem, or provided externally by
either the computer or terminal or finally two clocks would be provided
externally by the computer and terminal.
| Position A |
|
Switch Position B |
| 10 |
9 |
8 |
7 |
6 |
5 |
|
10 |
9 |
8 |
7 |
6 |
5 |
| 1 |
0 |
1 |
0 |
0 |
0 |
|
1 |
0 |
1 |
1 |
1 |
1 |
| 1 |
0 |
1 |
1 |
1 |
1 |
|
1 |
0 |
1 |
0 |
0 |
0 |
| 0 |
1 |
0 |
0 |
0 |
0 |
|
1 |
0 |
1 |
1 |
0 |
1 |
| 1 |
0 |
1 |
1 |
0 |
1 |
|
0 |
1 |
0 |
0 |
0 |
0 |
| 0 |
1 |
0 |
0 |
0 |
0 |
|
0 |
1 |
0 |
0 |
0 |
0 |
| 0=Off |
|
1=On |
274A is Clock Src
274B is Clock Src
Comp is Clock Src
Terminal is Clock Src
Both Units - ExCLK |
4.3 Asynchronous Mode
When operating the Model 274 in the Asynchronous Mode the following switches
must be set.
| |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
Speed (KBPS) |
| 274A |
1 |
1 |
1 |
0 |
0 |
0 |
1 |
DC to 38.4 |
| 274B |
0 |
0 |
0 |
0 |
0 |
0 |
1 |
DC to 38.4 |
| 274A |
1 |
1 |
1 |
1 |
0 |
0 |
1 |
DC to 19.2 |
| 274B |
0 |
0 |
0 |
1 |
0 |
0 |
1 |
DC to 19.2 |
4.3 Handshake Mode
The Model 274 can be set for one of two handshake modes. The first mode
allows for two full duplex control signals to be transmitted over the
single fiber to the far end. When S1 position 11 is 1 (On) then RTS and
DTR on the local side are passed through to CTS and DSR on the remote
end. The second mode performs a local loopback of the two control signals.
When S1 position 11 is 0 (Off) then RTS only affects CTS on the local
unit and DTR affects DSR and DCD on the local end. These control signals
are not passed through to the far side.
4.4 Loopbacks
The Model 274 is equipped with two loopback switches, Local and Remote
Loopback. Local Loopback allows a unit to be checked for operation while
the Remote Loopback verifies not only the unit but also the link connection
between units. When the Local Loopback switch is pressed any data that
is transmitted into the local unit is looped back and sent out on the
RD pin. In addition, the data is transmitted to the remote unit and synchronization
is maintained. When Remote Loopback is pressed any data that is transmitted
to the remote end is looped back and retransmitted back to the local unit
and is also passed to the RD pin of the remote unit.
4.5 Indicators
The Model 274 is equipped with a number of LED's that will help in the
installation and troubleshooting of a unit.
TD - the TD LED is connected to the transmit data pin, Pin 2 of the DB-25
connector, and will turn on when data is being received by the unit.
RD - the RD LED is connected to the receive data pin, Pin 3 of the DB-25
connector, and will turn on when data is being transmitted by the unit.
DCD - carrier detect. When S1 pin 11 is set to 0 (Off) then DCD will turn
on when synchronization between devices is established. When S1 pin 11
is set to 1 (On) then DCD will change according to the state of DTR on
the same unit.
Link - will turn on when synchronization between units is achieved.
5.0 Troubleshooting
The following is a list of possible problems that may arise during the
installation:
1. The Link LED is not on?
A) There is no connection between the 2 Model 274's.
B) One or both of the units are not powered. Check that both transformers
are plugged into a live outlet. To check the transformer a DMM or volt
meter will be required. Connect the meter with the ground connected to
the shaft of the 3.5mm connector and the lead to the tip of the transformer.
There should be a voltage greater than +12 VDC indicated on the meter.
C) There is a break in the fiber link.
2. TD LED will not turn on?
A) Verify that the input cable is configured properly.
B) The unit is not powered.
3. The TD LED on one side is on but there is no data being received
at the remote end?
A) Verify that the Speed switch is set the same as on both ends and the
Clock Source switches are configured properly.
B) The unit is not powered.
6.0 Power
The Model 274 derives its power from a small wall mounted adapter that
supplies 12 VDC to the unit. The Model 274 can be ordered to operate with
115 VAC, 60 Hz or with 220 VAC, 50 Hz.
7.0 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. 0315-0228
Rev. A
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.
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