Document No. 485LPRJ4500 - pg. 1/1
B&B Electronics Revised November 2000
This product designed and manufactured in USA of domestic and imported parts by
Port-Powered Half-Duplex RS-232 to RS-485 Converter
CE
Model 485LPRJ
The 485LPRJ is a port-powered half-duplex RS-232 to RS-485 converter. It
converts TD and RD RS-232 lines to balanced RS-485 signals. It supports two-wire
RS-485 communications only. The unit is powered from the RS-232 handshake lines,
DTR and RTS. The DTR handshake line must be high (asserted) to power the unit.
The RS-485 driver is enabled when RTS is asserted and disabled when RTS is
disasserted. The RS-485 receiver is disabled when the driver is enabled and is enabled
when the driver is disabled.
In order to maximize the amount of power available to the RS-485 driver, the RS-
232 handshake lines are not looped back (tied together). As a result the following handshake lines will appear as disasserted (low): CTS,
DCD, and DSR. Care should be taken to insure that any software being used doesn't require any of these handshake lines be asserted. If
existing software requires any of the handshake lines to be asserted, you can loop back the required handshake lines in your cable.
The RS-232 side has a DB-9 female connector. The RS-485 side has a six-position RJ11 connector.
Connections
Regardless of the system, the 485LPRJ must be connected with the proper polarity (See Table 1). With no data being sent and the driver
enabled, the RS-232 line should be negative and the Data(A) should be negative with respect to Data(B).
Proper operation of any RS-485 system requires the presence of a signal return path between the signal grounds of the equipment at
each end of an interconnection. This circuit reference may be established by a third conductor connecting the common leads of devices, or
it may be provided by connections in each equipment to an earth reference. When the circuit reference is provided by a third conductor , the
connection between the signal grounds and the third conductor should contain some resistance (e.g. 100 ohms) to limit circulating currents
when other ground connections are provided for safety.
Table 1 - 485LPRJ Pin-Outs
Biasing Resistors
The biasing resistors for the RS-485 receiver are 4.7K Ohm resistors. These resistors are labeled R1 and R6 (See Figure 1). Refer to
B&B Electronics' RS-422/485 Application Note for further information on biasing.
Specifications
Data Rate:
115.2K Baud max.
Power:
Port-powered from RTS and DTR
Dimensions:
3.0"L x 1.3"W x 0.9"H
Signal
RJ11 Pin #
Data A (-)
2
Data B (+)
5
Signal Ground
4
Figure 1
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 Number:
485LPRJ
Description:
Port-Powered Half-Duplex RS-485 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
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