B&B Electronics manual RS-422/RS-485 Connections/Operation

Chapter 6: RS-422/RS-485 Connections/Operation

These modes support 2 channels (transmit and receive). The pinouts of the DB-9 male connector are given in Table 4.

Table 4: RS-422/485 Pinouts

Name	Description	Direction	DB9M
			Pin
RD(A) −	Receive Data A	Input	1
TD(B) +	Transmit Data B	Output	2
TD(A) −	Transmit Data A	Output	3
GND	Signal Ground	------	5
RD(B) +	Receive Data B	Input	9

Connect only to specified pins for proper operation.

2-Wire RS-485 Connections

Fig. 6.1

2-WireRS-485 Mode: Your cables must bridge pins #1 & #3 and pins #2 & #9 in order to receive and transmit. Connect from Pin #2 to Data B(+) of your devices and from pin #3 to Data A(-) of your devices. Make sure your Mode/Jumpers are set, and that the driver Setting for DTR Operation is RS-485 Mode in the Device Manager.

Note that the EIA RS-422 Specification labels data lines with an "A" and "B" designator. Some RS-422 or RS-485 equipment uses a "−" and "+" designator. In most cases, the "A" line is the equivalent of the "−" line and the "B" line is the equivalent of the "+" line. Some device manufacturers may not follow the standard designation for RS-422 or RS-485, using the A connection for “+” and the B for “-“. In such cases, reversing the line pair permits operation.

Documentation Number 3PCIO1-0903 Manual Chapter 6 43

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