CM312 datasheet(26/56 Pages) ETC

26 / 56 page

CM312 Quad Serial utilityModule

RTD Embedded Technologies, Inc.

RS422 or RS485 Serial Port

You can change the mode switch to set the first port as RS422 or RS485. In this case, you must

connect CN3 to an RS422 or RS485 compatible device.

When using RS422 or RS485 mode, you can use the port in either half-duplex (two-wire) or full-

duplex (four-wire) configurations. For half-duplex (2-wire) operation, you must connect RXD+ to

TDX+, and connect RXD- to TXD-.

Note! Two 120-ohm termination resistors are provided on the utilityModule. Termination is

usually necessary on all RS-422 receivers and at the ends of the RS-485 bus. If the

termination resistor is required, it can be enabled by closing jumper JP8 5-6 for RxD

and/or 7-8 CTS.

RS422 and RS485 Mode Pinout

The following table gives the pinout of connector CN3 when RS422 or RS485 modes are enabled.

Table 9 Connector CN3 in RS422/485 Mode

CN3 Pin

Signal

Function

In/out

DB9

RTS-

Request to send (-)

Out

RTS+

Request to send (+)

Out

RXD-

Receive Data (-)

TXD+

Transmit Data (+)

Out

TXD-

Transmit Data(-)

Out

RXD+

Receive Data (+)

CTS-

Clear to send (-)

CTS+

Clear to send (+)

9,10

GND

Signal Ground

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