485LP9R

485LP9R Datasheet


Document No. 485LP9R1712 - pg. 1/2

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485LP9R 485LP9R 485LP9R (pdf)
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B&B ELECTRONICS

Document No. 485LP9R1712 - pg. 1/2

Port Powered RS-232 to RS-485 Converter

Model 485LP9R

The 485LP9R 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. One of these handshakes must be high asserted to power the unit See Table 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.

Table 1

RTS State DTR State

Functions Possible when port powering unit
none

High

Receive

High

Transmit

High

High

Transmit
* NOTE Low = disasserted and High = asserted

Connections A typical two wire RS-485 connected is shown in Figure Regardless of the system, the 485LP9R 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.

Figure 1

PRODUCT INFORMATION

Table 2 - 485LP9R Pin Outs

International Office 707 Dayton Road PO Box 1040 Ottawa, IL 61350 USA 815-433-5100 Fax 433-5104 European Office Westlink Commercial Park Oranmore Co. Galway Ireland +353 91 792444 Fax +353 91 792445

B&B ELECTRONICS

Document No. 485LP9R1712 - pg. 2/2

Signal

DB-9S Pin #

Transmit Data A -

Transmit Data B +

Receive Data A -

Receive Data B +

Signal Ground

Biasing Resistors

The biasing resistors for the RS-485 receiver are 4.7K Ohm resistors. These resistors are labeled R1 and

R6 See Figure Refer to B&B Electronics RS-422/485 Application Note for further information on biasing.

Figure 2

PRODUCT INFORMATION

Specifications Data Rate 115.2K Baud max.
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Datasheet ID: 485LP9R 520864