Document No. 422LP9TB4500 - pg. 1/2
B&B Electronics -- Revised November 2000
This product designed and manufactured in USA of domestic and imported parts by
Port Powered RS-232 to RS-422 Converter
CE
CE
CE
CE
Model 422LP9TB
The 422LP9TB 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 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). 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 422LP9TB can be used as an RS-232 to
RS-485 4-wire converter. To insure reception, it is recommended that DTR is asserted (or power the unit externally).
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.
Table 1
* NOTE: Low = disasserted and High = asserted
Connections
The 422LP9TB can be connected in three different type of systems: RS-422 (Figure 1), four-wire RS-485 (Figure 1),
and two-wire RS-422 (Figure 2). Regardless of the system, the 422LP9TB 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.
RTS
State
DTR
State
Functions Possible
(when port powering unit)
Low
Low
none
Low
High
Receive
High
Low
Transmit, Receive
High
High
Transmit, Receive
Document No. 422LP9TB4500 - pg. 2/2
B&B Electronics -- Revised November 2000
This product designed and manufactured in USA of domestic and imported parts by
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, 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.
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:
422LP9TB
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
Michael J. Fahrion, Director of Engineering
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