B&B Electronics 422LP9N Datasheet

Document No. 422LP9N0812 - 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, Receive

High

High

Transmit, Receive

The 422LP9N is a port-powered two-channel RS-232 to RS-422 converter. It converts TD and RD RS-232
lines to balanced RS-422 signals. The unit is powered from the RS-232 handshake lines DTR and RTS. One of
these handshake lines must be asserted (high) in order to power the unit (See Table 1). The RS-422 driver is
enabled when RTS is asserted. Therefore, RTS must be asserted in order to transmit data. The RS-422 receiver
is always enabled. If DTR is always asserted and the RTS is used to control the driver, the 422LP9N can be used
as an RS-232 to RS-485 4-wire converter. To insure reception, it is recommended that DTR is asserted.
In order to maximize the amount of power available to the RS-422 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-422 Converter

Model 422LP9N

Table 1

* NOTE: Low = disasserted and High = asserted

Connections
The 422LP9N can be connected in three different types of systems: RS-422 (Figure 1), four-wire RS-485

(Figure 1), and two-wire RS-485 (Figure 2). Regardless of the system, the 422LP9N 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-422 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.

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

Signal

DB-9S Pin #

Transmit Data A (-)

8

Transmit Data B (+)

3

Receive Data A (-)

2

Receive Data B (+)

7

Signal Ground

4, 6

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: 422LP9N
Description: 9-Pin Port-Powered RS-422 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

Document No. 422LP9N0812 - pg. 2/2

Table 2 - 422LP9N Pin-Outs

Biasing Resistors
The biasing resistors for the RS-422/RS-485 receiver are 4.7K Ohm resistors. These resistors are labeled

R1 and R6 (See Figure 3). Refer to B&B Electronics RS-422/485 Application Note for further information on
biasing.

Figure 3

Specifications

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

NOTE: If external power is required, apply power to DTR (4) and SG (5). Source must supply greater than 6VDC
and current limited to 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.