Document No. 485OT9L4300 pg. 1/3
B&B Electronics Revised November 2000
This product designed and manufactured in USA of domestic and imported parts by
9-Pin RS-232 to RS-485
Optically Isolated Converter
CE
CE
CE
CE
Model 485OT9L
Introduction
The Model 485OT9L is our most feature-packed RS-232 to RS-422/485 9-pin converter. It converts unbalanced, full or half-
duplex RS-232 signals to balanced, full or half-duplex RS-422 or RS-485 signals at baud rates up to 115.2 kbps. In addition, the unit
optically isolates and surge suppresses the RS-422/485 lines. The driver uses automatic SD (send data) or RTS (handshake) control,
or can be configured as always enabled for use in RS-422 systems.
A dipswitch selects communication features on the 485OT9L. Two LEDs show data traffic in either direction. Only one power
supply is necessary, located on the RS-232 side. The isolated power and ground on the RS-422/485 side are generated internally.
Connections are made through a DB9 female connector on the RS-232 side and terminal blocks on the RS-422/485 side. All
terminal blocks, dipswitches, and jumpers are located inside the hood and are reachable through the access panel, which slides closed
to protect the connections.
Description
The RS-232 port has a DB9 female connector with pins 3 (TD), 2 (RD), and 5 (Signal Ground) supported, pins 7 (RTS) and 8
(CTS) are tied together, and pins 6 (DSR), 1 (CD), and 4 (DTR), are also tied together. The 485OT9L has two LEDs: a Transmit Data
LED showing when data goes from the RS-232 side to the RS-485 side, and a Receive Data LED showing data going from the RS-485
side to the RS-232 side. These are very useful for determining if data is getting through the converter. The RS-485 terminal blocks
support Transmit Data (A) and (B), Receive Data (A) and (B), and Signal Ground. A single supply voltage of 10 to 30 VDC on the RS-
232 side powers the unit. An 8-position dipswitch allows the selection of baud rate, 2-wire or 4-wire mode, echo on or off, and
termination in or out.
RS-422/485 Driver Control
The 485OT9L uses either RTS Control or Send Data Control to enable the RS-485 driver. This option is user selectable by
setting push-on jumpers located next to the terminal blocks. RTS controls the driver using toggling Request to Send (pin 7) of the RS-
232 side. Raising RTS enables the driver and lowering RTS disables it. Automatic Send Data Control recognizes the first bit of data
from the RS-232 side, enables the transmitter and disables the receiver. After the last bit of data is sent from the RS-232 side, the
485OT9L waits one character length then disables the transmitter and enables the receiver. The timeout can be selected with
dipswitches or by changing the value of R21 (see Table 1). The timeout is preset at the factory for 9600 baud. Removing both sets of
jumpers completely will constantly enable the RS-485 driver. This makes the 485OT9L behave like an RS-422 converter. See Table 2
for standard communications settings.
Termination and Echo Options
Termination resistance can be selected with Switch 8 for high baud rates and long cable distances. See B&B Electronics RS-
422/485 Application Note for more information (available on the web site or request one by mail). The 4-wire/2-wire switches (6 and 7)
are turned off for 4-wire mode and on for 2-wire mode. When they are set on, they connect TD(A) to RD(A) and TD(B) to RD(B)
internally. Switch 5 controls Echo on and off. When switch 5 is in the off position the receiver is constantly enabled. Placing the switch
in the on position allows the driver or the receiver to be enabled at any time. In 2-wire mode it is recommended that switch 5 be turned
on to prevent data being sent out from "echoing" back through the receiver. Up to 32 receivers can be driven by any one RS-485
driver, allowing you to put together large systems with many drop points. Using an RS-422/485 repeater manufactured by B&B
Electronics can increase the number of receivers.
Table 1. Baud Rate Selection
Baud
Switch 1
Switch 2
Switch 3
Switch 4
R21
Time out (ms)
1200
OFF
OFF
OFF
OFF
820k
9.0
2400
OFF
OFF
OFF
OFF
410k
4.5
4800
ON
OFF
OFF
OFF
Not Used
2.2
9600
OFF
ON
OFF
OFF
Not Used
1.1
19200
OFF
OFF
ON
OFF
Not Used
0.6
38400
OFF
OFF
OFF
ON
Not Used
0.3
57600
OFF
OFF
ON
ON
Not Used
0.2
115200
OFF
OFF
OFF
OFF
8.2k
0.1
Document No. 485OT9L4300 pg. 2/3
B&B Electronics Revised November 2000
This product designed and manufactured in USA of domestic and imported parts by
Table 2. Standard Communications Settings
Communication Mode
JP1
Switch 5
Echo
Switch 6
4W/2W
Switch 7
4W/2W
RS-422 Mode
(full duplex)
Neither
OFF
OFF
OFF
RS-485 4-Wire Mode
(full-duplex)
RTS or SD
OFF
OFF
OFF
RS-485 2-Wire Mode
(half-duplex)
RTS or SD
ON
ON
ON
Specifications
Dimensions:
2.7 X 5.1 X 0.9 in (7.0 X 13.0 X 24.0 cm)
Temperature Range: 0C to 70C
Supply Voltage:
+10 to 30 VDC @ 95 mA maximum
Data Rates:
up to 115.2 kbps
Connectors:
DB9 female for RS-232
Terminal blocks for RS-422/485 and power
Isolation:
2000 VAC optical isolation of data signals
and ground
Surge Suppression:
7.5V, bi-directional avalanche breakdown device.
500W peak power dissipation
Clamping time <1 picosecond (theoretical)
DECLARATION OF CONFORMITY
Manufacturer's Name:
B&B Electronics Manufacturing Company
Manufacturer's Address:
P.O. Box 1040
707 Dayton Road
Ottawa, IL 61350 USA
Model Numbers:
485OT9L
Description:
RS-232/485 Optically Isolated Converter
Type:
Light industrial ITE equipment
Application of Council Directive:
89/336/EEC
Standards:
EN 50082-1 (IEC 801-2, IEC 801-3, IEC 801-4)
EN 50081-1 (EN 55022, IEC 1000-4-2)
EN 61000 (-4-2, -4-3, -4-4, -4-5, -4-6, -4-8, -4-11)
ENV 50204
EN 55024
Michael J. Fahrion, Director of Engineering
Typical RS-422/485 2 W ire Setup
D a ta B +
D a ta A -
R D A -
RS-232
GND
10 - 30
VDC
GND
422/485
R D B +
R t
SW
8
Pow er
Supply
-
+
T D A -
T D B +
SW
7
SW
6
485OT9L
R t
GND
Dr.
Rec.
E n a b l e
2 W ir e D e v ic e
T yp ical R S -422 /48 5 4 W ire S e tup
T D A -
T D B +
R D B +
R D A -
R D A -
RS-232
GND
10 - 30
VDC
GND
422/485
R D B +
R t
SW
8
Power
Supply
-
+
485O T 9L
T D A -
T D B +
SW
6
SW
7
R t
GND
Dr.
R ec.
E n a b l e
4 Wire Device
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