Document No. 422LP9R4500 - 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 422LP9R
The 422LP9R 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 422LP9R can be used as a 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.
Table 1
* NOTE: Low = disasserted and High = asserted
Connections
The 422LP9R can be connected in three different type of systems: RS-422 (Figure 1), four-wire RS-485 (Figure 1),
and two-wire RS-485 (Figure 2). Regardless of the system, the 422LP9R 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.
TD(A) -
RD(B) +
RD(A) -
G N D
TD(B) +
4 2 2 L P 9 R
8
TD(A) -
RD(B) +
RD(A) -
G N D
TD(B) +
7
1 0 0
4
3
2
4 2 2 L P 9 R
G N D
RD(A) -
TD(B) +
TD(A) -
RD(B) +
1 0 0
RS-422 or
4-wire RS-485
Figure 1
G N D
RD(A) -
TD(B) +
TD(A) -
RD(B) +
2-wire RS-485
8
7
1 0 0
4
3
2
1 0 0
Figure 2
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. 422LP9R4500 - pg. 2/2
B&B Electronics -- Revised November 2000
This product designed and manufactured in USA of domestic and imported parts by
Table 2 - 422LP9R 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.
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:
422LP9R
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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