B+B SmartWorx FOSTC Quick Start Manual

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QUICK START
GUIDE

Doc ument N umber : 710 -112 07-00 _F OSTC _2217qs g

Before you begin, be
sure you have the following:

Model FOSTC

High Speed RS-232/422/485

Fiber Optic Modem

+ FOSTC Fiber Optic Modem
+ 12 VDC, 140 mA Power Supply
(sold separately)

Recommended Accessories

12 VDC Power Supply, 6 W,
Int’l AC Input, 2.5mm Plug

# SMI6-12-V-P230-C1

Serial Adapter Cable,
DB9F to DB25M, 6 ft (1.8m)

# 232CAM

FOSTC Circuit Diagram

4

Because RS -422 and RS-485 s ignals are also available o n the same
connector, take spec ial care not to hook any externa l signals to these
pins. This is no t a problem for most serial d evices, but a custom cable
must be made that d oes not connect to the extra pi ns on the DB25
connector if yo ur device has power or special no n-standard outputs .

Figure 1. Fiber Point-to- Point & Multi-Drop Ring Diagrams

Power Jack

Product Overview

Fiber Optic
Inherent EMI/RFI &
Transient Immunity

FOSTC Specications Table

Transmission Dual multi- mode ber optic cab le

Point-to-point Asynchronous, half- or full-duplex

Multi-drop Asynchronous, half-duplex ber ring

Serial Interface RS-232, RS- 422, RS- 485

Power
Connection

2.5mm phone jack (tip positi ve)
or DB25 pins 25(+) and 12(-)

Temperature -40 to 80 °C (-40 to 176 °F) operat ing

MTBF 570522 hours

Getting Started

1

The FOSTC provides the most versatile connection
possible between asynchronous serial equipment using

ber optic cable. Applications include point-to -point

communications between serial devices or a multi-drop

ber ring conguration allowing multiple serial devices to

communicate with each other.

It allows any two pieces of asynchronous serial equipment

to communicate full or half-duplex over two bers at

typical distances up to 2.5 miles (4 km).

Fiber Optic -

ST Connectors

RS-232/422/485

DB25 Female

RS-232 Connections

3

RS-422 & RS- 485 Connections

4

The RS- 422/485 driver and receiver are connected to 4
pins on the DB25 connector. Signal ground is on Pin 7.

When connecting to a four-wire RS- 422/485 device or
system, connect the output of your device to pins 16 (B or
+) and 17 (A or +). Connect the input to your device to pins
14 (B or +) and 15 (A or -).

For two-wire RS-485 systems, the driver and receiver
must be connected together by tying pins 14 and 16
together and 15 and 17 together. This allows the FOSTC
to communicate half-duplex over the same pair. See
Figure 3 for connection diagrams to your RS- 422 or RS­485 equipment.

If termination is needed, a spot on the PCBD of the
FOSTC labeled “Rt” allows you to solder a termination
resistor across RD(A) and RD(B) lines. Removing R8 and
R16 and replacing them with through-hole components
can also change the off-state bias resistor values.

RS-232 signals are pinned as a DCE device (input on Pin 2
and output on Pin 3).

• A straight-through cable can be used from your DB25
port on any DTE device such as a PC or terminal.

• A standard 9 to 25-pin adapter can be used in cases
where the serial port on the DTE device is a DB9.

• A null modem cable or adapter that swaps pins 2 and 3 is
needed for connecting to modems or other DCE devices.

See Figure 2 for connection diagrams to 9 -pin and 25 -pin
DTE and DCE devices.

Figure 2. RS-232 Connection Diagrams

Fiber Optic Connections

2

The FOSTC uses a separate LED emitter and photo­detector operating at 820 nm wavelength. Connections to
the emitter and detector are on ST type connectors.

The FOSTC uses a separate LED emitter and photo­detector operating at 820 nm wavelength. Connections to
the emitter and detector are on ST type connectors.

Almost any multimode glass ber size can be used including

50/125 µm, 62.5/125 µm, 10 0/140 µm, and 200 µm. One

ber is required for each connection between a transmitter

and receiver.

In a point-to-point conguration, two bers are required
between the two modems - one for data in each direction.

In a multi- drop ring conguration, one ber between TX

and RX around the loop is required.

Before making modications to the FOSTC, consult B+B Smart Worx’ free

“RS- 422/485 Applicati on Note” or other sources of info rmation to see if
termination is necessary. Available at: www.advantech- bb.com

RS- 422 & RS- 485 Connections - continued

RS-422/485 Connection Diagrams

DIP Switch Set Up

5

The Dip Switch (SW1) denes the mode of operation when

being used for RS-422 or RS-485.

Positions 1 through 5 determine the timeout of the RS­485 driver. Because the driver is controlled by hardware, a

specic time must be set in order to tell the hardware how
long to wait for data on the ber side before turning off the

RS-422/485 driver.

If this time is set too short, the driver could be disabled
before transmission is complete, resulting in data corruption.

If the time is set too long, the RS-485 device may respond
before the RS- 422/485 driver in the FOSTC is disabled,
corrupting this response.

It is recommended that the timeout be set for approximately
one character time or longer. The character times for several
different baud rates are selectable on switch positions
1 through 5. If you need a different timeout than what is
provided, R10 can be removed and replaced with a different
value R9. Table 1 shows different timeout values for the
switch positions as well as typical R9 replacement values.

Position 6 of SW1 sets the unit in “Multidrop” mode or “Point­to-Point ” mode. See Figure 3 for typical system setups using
the FOSTC in different modes.

• When set in Multidrop Mode, data arriving on the

ber optic receiver is repeated back out the transmit ter.

Position 6 must be turned “On” when the FOSTC is to

be used in a multi-drop ring conguration.

• When set in Point-to-Point Mode, data arriving at

the ber optic receiver is not sent back out the ber

optictransmitter. Position 6 must be turned “Off” when
the FOSTC is to be used as either end of a point-to­point communication line.

Positions 7 and 8 of SW1 determine when the RS- 422/485
driver and receiver are enabled. Position 7 controls the
driver and Position 8 controls the receiver. Tab le 2 illustrates
the switch settings for typical setups.

• For RS-485 two-wire systems, both switches should
be in the “On” position. This disables the RS-422/485
receiver whenever the driver is enabled, preventing data

from being echoed back to the ber side of the FOSTC.

• For multi-drop RS-485 four-wire systems, position
7 should be “On” and position 8 should be “Off.” This
allows the receiver to be enabled all of the time and
eliminates some possible timing problems.

• For RS-422 operation, set both switches to the “Off”
position.

Table 1. RS-485 Timeout Selection

BAUD

RATE

Pos. 1Pos. 2Pos. 3Pos. 4Pos.

5

R9

Time

(ms)

1200

ON Off Off Off Off 830 kΩ 8.20

2400

ON Off Off Off Off 430 kΩ 4.30

4800

Off Off Off Off ON Not Us ed 2.20

9600

Off Off Off ON Off Not Us ed 1.3 0

19.2k

Off Off ON Off Off Not Us ed 0.56

38.4k

Off ON Off Off Off Not Us ed

0.27

57.6k

ON Off Off Off Off Not Used

0.22

76.8k

ON Off ON ON Of f Not Used

0.1 4

115.2k

ON ON ON Off Of f Not Used

0.1 0

153.3k

ON Off Off Off Off 6.3 kΩ

0.06

230.4k

ON Off Off Off Off 4.3 kΩ

0.04

460.8k

ON Off Off Off Off 2.2 kΩ

0.02

Table 2. RS-422/485 Switch Settings

Position 8
TX Enable

Position 8
RX Enable

RS-485 2-Wire Mode

(half-duplex)

ON ON

RS-485 4-Wire Mode

(full-duplex)

ON Off

RS-422 Mode

(full-duplex)

Off Off

Multi-Drop Operation

6

A multi-drop conguration is created by forming a ring of

FOSTCs (see Figure 1, Multi-drop Ring). Whichever serial
device sends data, all other devices receive it. The data is

repeated around the ber ring until it reaches the source,

where it is blocked. There is no echo back to the serial side
of the sending device.

Each ber transmitter must be connected to the following

converter’s receiver. Set SW1:6 to the “On” position on all
FOSTCs in the ring.

Any device can be full-duplex (RS-232, RS- 422, or four-wire
RS-485) or half duplex RS-485. Because all data shares the
same path on the ring, only one device can send data at a
time.

Interfacing to Fiber Devices
from other manufacturers

7

NOTE: The factory default for the LED emitter is to have the
light “On” in the idle state. To interconnect with other devices
that have the light “Off” in the idle state, this unit would need

to be modied. To modify the unit so that the light is “Off” in

the idle state, contact B+B SmartWor x Technical Support.

Typical Installation Conguration

8

Below is a University Campus setup that illustrates the basic conguration of a typical Fiber Optic Network. This
scenario uses a combination of B+B SmartWorx ber devices, including: 3 x Model FOSTC serial/ber conver ters, 2 x
Model FOSTDRP ber repeaters, and 1 x Model FOSTCDR DIN-rail mount ber converter. Each of the items requires

a power supply (not shown).

Note 1: For the total transmi ssion time over lon g bers, the time to tr ansverse the
ber must be cons idered if delay is an iss ue. Light takes about 8. 05 microse conds
to travel over 1 mile of ber.

Note 2: When operat ing in a ring cong uration, eac h node in addition to th e two
in the point-to -point specicat ion adds an additi onal 100 to 200 nano seconds of

del ay.

Note 3: When operat ing in a ring cong uration, eac h node in addition to th e two in
the point-to -point specica tion adds an additi onal 50 to 70 nanosec onds of skew.

Note 4: When operat ing in a ring congu ration, each se rial device mu st wait at

least this minimum time between receiving data from the ring and transmitting
back on to it.

Table 4. Recommended Maximum FOSTC’s
In A Fiber Ring Topology

BAUD RATE

RS-232

OPERATION

RS-422/485

OPERATION

460.8 kbps n/a 2

230.4 kbps n/a 4

115.2 kbps 2 8

57.6 kbps 8 16

38.4 kbps 16 24

19.2 kbps and lower 32 32

Table 3. Transmission Paramters

PARAMETER Min.

Typ ical Max. Conditions

Data Rates (RS-232 Operation) 0 bps - 115.2 kbps -

Data Rates (RS-422/485 Operation) 0 bps - 500 kbps -

Power Supply Voltage 10 VDC 12 VDC 14 VDC -

Power Supply Current Draw - 14 0 mA

Full RS -485

termination

Optic Wavelength - 820 nm - -

Fiber TX Launch Power -17 dB m -13 dBm -10 dBm -

Minimum Required Fiber RX Power - -25.4 dBm -24 dBm -

Maximum Receiver Power - - -10 dBm -

Coupled Power Budget - 12.1 dBm - -

Fiber Range - 2.5 mi. - -

End-to-End Delay - 2000 ns 2650 ns

Point-to-po int
RS-232 operation
(See Notes 1 & 2)

End-to-End Delay - 550 ns 1000 ns

Point-to-po int

RS-422/485 operation

(See Notes 1 & 2)

End-to-End Skew - 9 00 ns 1100 ns

Point-to-po int
RS-232 operation

(See Note 3)

End-to-End Skew - 50 ns 120 n s

Point-to-po int

RS-422/485 operation

(See Note 3)

Maximum Total Diber Ring Length - - 5 mi. (See N ote 1)

Delay betw. RX & TX on Fiber Ring 52 µs - - (See Note 4)