Contents:

- Hardware Configuration
- Setting Up the RS485/422 Interface (Software)
- Setting Up the RS485/422 Interface (Hardware)
- Isolation Protection
- DIP Switch Settings

A Phoenix 8-pin inline terminal connector in place of a DB-25 RS232 connector identifies an EtherPAD as having a RS485/422 serial interface.



RS422/485 Serial Application Interface

Operating Modes
The RS422/485 EtherPAD supports the following operating modes:
- Point-to-Point/4-wire Full Duplex.
- Point-to-Point/2-wire Half Duplex
- Multidrop/4-wire Full Duplex.
- Multidrop/2-wire Half Duplex.

Setting Up the RS485/422 Interface (Software)

Modifying Serial parameters
Web Browser



Click on the Change link to change Serial parameters

Serial/Telnet



Select the option you wish to configure to change Serial Parameters

The following options are configurable:
Serial Interface - the name of the serial interface currently being configured.
Data Bits - the number of data bits (5, 6, 7 or 8). The default is 8.
Stop Bits - the number of stop bits (1 or 2). The default is 1.
Parity - error checking. The default is None.
Speed - data transfer rate.
Flow Control - handshaking. Supported types are Hardware (RTS/CTS) and Software (Xon/Xoff).

Important: Hardware (RTS/CTS) flow-control cannot be used when the Connection Type is set to RS485 or RS422. Software flow-control cannot be used when the Connection Type is set to RS485.


Connection Type - the type of serial connection to be used.
- RS232 - full-duplex direct serial connection to the device.
- RS422 - full-duplex 4-wire serial connection to the device.
- RS485 - half-duplex 2-wire serial connection to the device.
- Modem - indicates that a modem device is connected to the serial port.
- Protocol - the protocol to be used to communicate with the serial device.

Available protocols are dependent on the optional features enabled:
o Raw - no protocol is used and data is streamed transparently.
o TC500 - the Burroughs TC500 Poll-Select protocol (as currently used with ATM's)
o PPP - the serial interface will be used as a PPP interface.
o Modbus/ASCII - the Modbus protocol using ASCII framing. Refer to Modbus configuration.
o Modbus/RTU - the Modbus protocol using RTU framing. Refer to Modbus configuration.

Setting Up the RS485/422 Interface (Hardware)

Impedance Matching and Termination Resistors

When an electrical signal travels through two different resistance junctions in a transmission line, the mismatch will sometimes cause signal reflections. This reflection causes signal distortion that contributes to communication errors. The solution to this problem is to establish the same impedance at the line ends as in the line itself by terminating the line ends with resistors. Normally it will be sufficient when the value of the termination resistor equals the characteristic impedance of the transmission lines. The resistors should then be added near the receiving side.



Note: { - Represents a terminating Resistor near the receiving side. The suggested termination resistor is 100 ohm.

Isolation Protection

The RS485 EtherPADs provide isolation protection, which protects against high voltages up to 2000 V.

DIP Switch Settings










Illustration of Switch Functions






Note: Either of the 4-Wire pairs can be used in 2-Wire operation.