ATC 277SM User Manual
High-Speed RS-232/RS-485/RS-422
Single-Mode Fiber Optic Modem
User’s Manual
MODEL-277SM
(English Rev 2.2)
1.0 Description
The MODEL 277SM was designed to provide the most
versatile connection possible between any asynchronous
serial equipment using Fiber Optic cable. It allows any two
pieces of asynchronous serial equipment to communicate full
or half-duplex over two fibers at typical distances up to
20KM.
RS-232 data signals at up to 115.2Kbps and RS-422, or
RS-485 data signals at up to 250Kbps are supported.
Different standards can be mixed and matched to allow
RS-232 devices to connect to your RS-422 or RS-485
system. This means the MODEL 277SM can replace
converters and isolators when connecting remote devices,
while providing the EMI/RFI and transient immunity of optical
fiber.
The MODEL 277SM supports both the Transmit and Receive
data lines, and provides full hardware control of the RS-422
/485 driver with automatic Send Data Control circuit.
Timeouts are auto detect between 0.10 and 2.2 ms. All serial
connections are provided on the DB-9 male connector or
6-bit terminal, while the single-mode fiber is connected via
two SC/ST/FC connectors. The unit is powered by 9-24 VDC
at 250 mA max.
2.0 RS-232 Connections
Connection of the MODEL 277SM is simple and straight
forward. The DB9 male serial connector is used for connect
to RS-232 interface. The RS-232 signals are defined as a
DTE device (input on Pin 2 and output on Pin 3)
Table 1:RS-232 Connection Diagrams
DB-9 Male
(PIN)
RS-232
2 RXD
3 TXD
5 GND
3.0 RS-422 & RS-485 Connections
Table 2:RS-422/RS-485 Connection Diagrams
6-Bit
Terminal
RS-422 RS-485
PIN1 T+ 485+
PIN2 T- 485PIN3 R+ NC
PIN4 R- NC
PIN5 VIN VIN
PIN6 GND GND
4.0 Fiber Optic Connections
The MODEL277SM uses a separate LED emitter and
photo-detector operating at 1310nm wavelength Connections
to the emitter and detector are on SC/ST/FC type connectors.
One fiber is required for each connection between a
transmitter and receiver. In a point-to-point configuration, two
fibers are required between the two modems, one for data in
each direction.
The most important consideration in planning the fiber optic
link is the “power budget” of the fiber modem. This value
represents the amount of loss in dB that can be present in
the link between the two modems before the units fail to
perform properly. This value includes line attenuation as well
as connector loss. For the MODEL277SM the typical
connector-to-connector power budget is 13 dB. Because
9/125um Single Mode Fiber cable typically has a line
attenuation of 0.6 dB per Km at 1310 nm, the 13 dB power
budget translates into 20 KM..
5.0 Specifications
Transmission Line: Dual Single-mode optical cable
Point to Point Transmission: Asynchronous, half
or full-duplex
Interfaces: RS-232, RS-422, or RS-485
Data Rates: RS-232 0 to 115.2KBPS
RS-422/485 0 to 250KBPS
Distance : RS-485/RS-422 0-1.2Km
Fiber Typical Range: Up to 20Km on Single mode glass
fiber
Coupled Power Budget: 15.0 dB
Optic Wavelength: 1310 nm
Fiber Connector: SC(ATC-277SM-SC)
ST(ATC-277SM-ST)
FC(ATC-277SM-FC)
Connectors: DB-9 male for RS-232, 6-Bit terminal for
RS-422/485 connection,
Power Supply: Requires 9 – 24V VDC @ 250 mA
max.
Operation temperature:-40℃-70℃
EMI and Safety: CE，FCC Class A
Dimensions: 96 Lx 66W x 26H(mm)
Weight: 0.40Kg
6.0 Order Information.
Table 3: Order Information
P/N:
Fiber
Type
Wavelength
(nm)
Fiber
Length(Km)
ATC-277SM-SC SC 1310 20
ATC-277SM-ST ST 1310 20
ATC-277SM-FC FC 1310 20
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