422LP25R-0812-1/2
© 2003 by B&B Electronics. All rights reserved.
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
PRODUCT INFORMATION B&B ELECTRONICS
Model 422LP25R
Port-Powered RS-232 to RS-422
Converter
with DB-25 Connectors
This RS-232 to RS-422 converter converts unbalanced RS-232 signals to balanced RS-422 signals. The power used
for this converter is derived from the transmit data line (pin 2) and the handshake control lines (pins 4, 5, 6, 8, and 20).
The converter can derive power from these lines when they are in the positive or negative voltage state. This permits
the converter to be used in applications without any regard to software control of the handshake lines. If no handshake
lines are available and all power must be derived from the transmit data line, the converter can drive limited cable
lengths. A guide for this condition would be to drive only several hundred feet of transmission line and not to terminate
the transmission line with a resistor of less than 1000 ohms. When more handshake lines are available longer lengths
of cable can be driven. This converter has been tested at 115.2k baud with 4000 feet of cable. For applications where
handshake lines are not available and long cable runs are involved, an external power supply can be connected to the
male connector on the RS-422 side of the converter on pins 12 (Gnd) and 25 (+12).
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.
The RS-232 port uses a female DB-25 type of connector with pins 2 (TD input) and 3 RD(RD output) supported. Signal
Ground is pin 7 on both the RS-232 and RS-422 sides.
Interconnection of the converter with another RS-422 device
1. The polarity of the two RS-422 lines must be correct. With no data being sent, the RS-232 line should be negative
and the RS-422 "A" pin 2 should be negative with respect to the "B" pin 14.
2. The wire recommended in the RS-422 Standard is number 24 AWG copper conductor, twisted-pair telephone
cable with a shunt capacitance of 16 pF per foot.
3. For long runs and/or high data rates it is recommended that the wires be terminated with a resistor at the receive
end. The twisted pair usually used has an impedance of about 100 ohms, therefore a 100 ohm resistor is normally
used for the termination. The RS-422 side of the converter requires more power as the transmission line is
increased and as the termination resistor value is reduced, therefore it may be necessary to use a termination
resistor that is larger than 100 Ohms.
The RS-422 driver has the ability to drive 10 RS-422 receivers connected in parallel. A system of multiple receivers
may require some experimentation with location and size of termination resistors, line lengths, grounding, etc.
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: 422LP25R
Description: Port-Powered RS-422 Converter
Type: Light industrial ITE equipment
Application of Council Directive: 89/336/EEC
Standards: EN 55022
EN 61000-6-1
EN 61000 (-4-2, -4-3, -4-4, -4-5, -4-6, -4-8, -4-11)
Robert M. Paratore, Director of Engineering
(2 pages)
(2 pages)
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