Bb-electronics 422LP9N - Datasheet User Manual download pdf

Document No. 422LP9N0812 - pg. 1/2

www.bb-elec.com [email protected] sup[email protected]

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PRODUCT INFORMATION B&B ELECTRONICS

Port Powered RS-232 to RS-422 Converter

Model 422LP9N

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.

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.

RTS

State

DTR

State

Functions Possible

(when port-powering unit)

Low

none

Low

High

Receive

High

Low

Transmit, Receive

High

Transmit, Receive

1 2

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