CHAPTER 7
RS422/RS485 CABLING INFORMATION

7.1 RS422 Cabling Information for DB25

The communication interface follows the EIA RS422 standard. The signal assignments for a standard DB25 connector are shown below:

Pin

Description

1

Chassis Ground (GND)

2

Request to Send-(RTS-)

3

Request to Send+(RTS+)

4

Clear to Send-(CTS-)

5

Receive Data+(RxD+)

6

Clear to Send+(CTS+)

7

Transmit Data-(TxD-)

8

Signal Ground (SG)

20

Transmit Data+(TxD+)

22

Receive Data-(RxD-)

To connect the RS422 to other DATA TERMINAL EQUIPMENT (DTE) devices, the developers recommend using a DTE to DTE connection as shown below.

HOST

REMOTE

    Signal Ground

    Signal Ground

    Transmit Data(+)

    Receive Data(+)

    Receive Data(+)

    Transmit Data(+)

    Transmit Data(-)

    Receive Data(-)

    Receive Data(-)

    Transmit Data(-)

    Request to Send(+)

    Clear to Send(+)

    Clear to Send(+)

    Request to Send(+)

    Request to Send(-)

    Clear to Send(-)

    Clear to Send(-)

    Request to Send(-)

7.2 RS422 Cabling Information for DB9

The communication interface follows the EIA RS422 standard. The signal assignments for a standard DB9 connector are shown below :

Pin

Description

1

Signal Ground (SG)

2

Request to Send+(RTS+)

3

Request to Send-(RTS-)

4

Transmit Data+(TxD+)

5

Transmit Data-(TxD-)

6

Clear to Send+(CTS+)

7

Clear to Send-(CTS-)

8

Receive Data+(RxD+)

9

Receive Data-(RxD-)

7.3 RS485 Cabling Information for DB25

The RS485 signal assignment is shown as follows.

Pin

Description

7

Transmit Data-/Receive
 Data-(TRD-)

8

Signal Ground(SG)

20

Transmit Data+/Receive
 Data+(TRD+)

The RS485 communication is based on cable sharing method, which is connected as following:

Computer at site 1

Computer at site 2

TRD+

TRD+

TRD–

TRD–

Ground

Ground

7.4 RS485 Cabling Information for DB9

The RS485 signal assignment is shown as follows.

Pin

Description

1

Signal Ground

4

Transmit Data+/
Receive Data+(TRD+)

5

Transmit Data-/
Receive Data-(TRD-)