B&B Electronics 485LP9TB Datasheet

Document No. 485LP9TB0812 - pg. 1/2

www.bb-elec.com [e-mail] [e-mail]

International Office: 707 Dayton Road PO Box 1040 Ottawa, IL 61350 USA 815-433-5100 Fax [phone]

European Office: Westlink Commercial Park Oranmore Co. Galway Ireland [phone] Fax [phone]

PRODUCT INFORMATION B&B ELECTRONICS

RTS

State

DTR

State

Functions Possible

(when port powering unit)

Low

Low

none

Low

High

Receive

High

Low

Transmit

High

High

Transmit

The 485LP9TB is a port-powered two-channel RS-232 to RS-485
converter. It converts TD and RD RS-232 lines to balanced RS-485 signals.
The unit can be powered from the RS-232 handshake lines, DTR and RTS. If

port powering the unit, one of these handshake lines must be asserted (high) in
order to power the unit (See Table 1). DTR must be asserted to receive data. 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.

Port Powered RS-232 to RS-485 Converter

Model 485LP9TB

Table 1

* NOTE: Low = disasserted and High = asserted

Connections
A typical two wire RS-485 connected is shown in Figure 1. Regardless of the system, the 485LP9TB must

be connected with the proper polarity. With no data is being sent and the driver enabled, the RS-232 line should
be negative and the TD(A) should be negative with respect to TD(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.

Biasing Resistors

The biasing resistors for the RS-485 receiver are 4.7K Ohm resistors. These resistors are labeled R1 and
R6 (See Figure 2). Refer to B&B Electronics RS-422/485 Application Note for further information on biasing.

Document No. 485LP9TB0812 - pg. 2/2

www.bb-elec.com [e-mail] [e-mail]

International Office: 707 Dayton Road PO Box 1040 Ottawa, IL 61350 USA 815-433-5100 Fax [phone]

European Office: Westlink Commercial Park Oranmore Co. Galway Ireland [phone] Fax [phone]

PRODUCT INFORMATION B&B ELECTRONICS

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: 485LP9TB
Description: 9-Pin Port-Powered 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

Robert M. Paratore, Director of Engineering

Figure 2

Specifications

Data Rate: 115.2K Baud max.
Power: Port Powered from RTS and DTR.

Note: If external power is required, use a source that can supply 12 to 16VDC at 40mA

NOTE: When using an external supply, the supply should be connected only to specifically labeled power
inputs (power jack, terminal block, etc.). Connecting an external power supply to the handshake lines may
damage the unit. Contact technical support for more information on connecting an external power supply
to the handshake lines.