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 DB25 connector are shown below:

Pin
 Description
1
     Chassis Ground
7
     Signal Ground(SG)
12
     Transmit Data+(TxD+)
13
     Receive Data+(RxD+)
24
     Transmit Data-(TxD-)
25
     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
    Ground
     Ground
    Signal Ground
     Signal Ground
    Transmit Data(+)
     Receive Data(+)
    Receive Data(+)
     Transmit Data(+)
    Transmit Data(-)
     Receive Data(-)
    Receive Data(-)
     Transmit Data(-)


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
2
     Receive Data+(RxD+)
3
     Transmit Data+(TxD+)
4
     Transmit Data-(TxD-)
5
     Signal Ground(SG)
6
     Receive Data-(RxD-)


7.3 RS485 Cabling Information for DB9
The RS485 signal assignment is shown as follows.

Pin
 Description
2, 3
     Transmit Data+/ Receive Data+(TRD+)
5
     Signal Ground
4, 6
     Transmit Data-/Receive Data-(TRD-)

TRD+ signal means short pin 2 and pin 3, and TRD- signal means short pin 4 and pin 6. 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