StarTech IC485S/GB/EU Communication Guide

Help Contents

Introduction

The IC485S/GB/EU is an RS-232 to RS-422/RS-485 converter:

StarTech IC485S/GB/EU RS-232 to RS-422/RS-485 converter

The information in this article applies to a range of converters:

The remainder of this article uses the name IC485S to refer to any of the above.

The converter has two switches that configures how it operates:

RS-422 mode

In RS-422 mode two pairs of wires are used to communicate with the PLC device. For example:

IC485S showing an RS-422 point to point link

The communication link is full duplex. The Rx pair of wires handles data sent from the PLC to Fernhill SCADA. The Tx pair of wires handles data from from Fernhill SCADA to the PLC. Data can be sent in both directions at the same time.

Adapter setup

To configure the IC485S for RS-422 mode:

  1. Set SW1 to DCE mode.
  2. Set SW2 to T.on/R.on (transmit and receive permanently on).

RS-232 Computer Communication Cable for RS-422 Mode

You can use a typical DB-25 to DE-9 modem cable to connect the IC485S adapter to an RS-232 DE-9 port on a computer.

As an alternative you can create your own cable using this wiring:

IC485S
D-Subminiature connector DB-25 plug wiring side shown
Computer
D-Subminiature connector DE-9 socket wiring side shown
TxD22RXD
RxD33TXD
GND75GND

In RS-422 mode only the RXD, TXD and GND signals are required on the RS-232 link.

RS-422 Connection

For best results use a connection cable with four wires arranged as two twisted pairs. Use one twisted pair for the transmit circuit and the other twisted pair for the receive circuit. For a long connection cable install termination resistors at each end of the cable.

Use this table to select the correct wiring between the IC485S and various PLC Devices:

StarTech
IC485S
IC485SGB
IC485SEU
1 (TX-) 2 (TX+) 3 (RX+) 4 (RX-)
Mitsubishi Melsec
RDB RDA SDA SDB
Omron CS/CJ DE-9
SCB41-V1 Port 2
SCU31-V1 Port 1
SCU31-V1 Port 2
SCU41-V1 Port 1
6 (RDA) 8 (RDB) 2 (SDB) 1 (SDA)
Omron CS/CJ Terminals
SCU32 Port 1
SCU32 Port 2
SCU42 Port 1
1 (RDA) 2 (RDB) 4 (SDB) 3 (SDA)
Omron CP1x
CP1W-CIF11
RDA- RDB+ SDB+ SDA-
Omron C200H
C200H-LK202-V1
6 (RDA) 1 (RDB) 5 (SDB) 9 (SDA)
Omron CPM1/2
CPM1-CIF11
RDA RDB SDB SDA
Wago 750
750-312
750-315
7 (RxD Inv) 2 (RxD) 3 (TxD) 8 (TxD Inv)

Note: The labels applied to RS-422 connections are not consistent and vary from one manufacturer to another.

Use these guides for information about RS-422 connections on PLC Devices:

RS-485 mode

In RS-485 mode one pair of wires is used to communicate with the PLC device. For example:

IC485S showing an RS-485 multi-point link

The communication link is half duplex. Only one device can transmit at any one time.

Adapter Modes

In RS-485 mode only one device can transmit at any one time. Each device must enable its transmitter only when it needs to send data.

Setting SW2 to T.RTS/R.RTS configures the IC485S to control the transmit and receive functions as follows:

RTSTransmitReceive
InactiveOffOn
ActiveOnOff

Adapter Setup for RS-485 Operation

To configure the IC485S for RS-485 mode:

  1. Set SW1 to DCE mode.
  2. Set SW2 to T.RTS/R.RTS (transmit if RTS active, receive if RTS inactive).

RS-232 Computer Communication Cable for RS-485 Mode using RTS Control Mode

You can use a typical DB-25 to DE-9 modem cable to connect the IC485S adapter to an RS-232 DE-9 port on a Computer.

As an alternative you can create your own cable using this wiring:

IC485S
D-Subminiature connector DB-25 plug wiring side shown
Computer
D-Subminiature connector DE-9 socket wiring side shown
TX23TXD
RX32RXD
RTS47RTS
GND75GND

RS-485 Connection

For best results use a twisted pair cable. For a long connection cable install termination resistors at each end of the cable.

Connect these signals on the IC485S to the RS-484 interface on the PLC Device:

IC485SPLC Device
1 (TX-), 4 (RX-)Data-
2 (TX+), 3 (RX+)Data+

Use these links for information about RS-485 connections on PLC Devices:

Fernhill SCADA Serial Port Mode

When configuring the Mode property of a serial communication channel in Fernhill SCADA be sure to set RTS mode to tg. For example:

Baud=9600 Data=8 Parity=E Stop=2 RTS=tg

Setting RTS=tg tells the Fernhill SCADA driver to assert the RTS signal when sending data. This in turn tells the IC485S to turn on the RS-485 transmitter during the send.

Further Information

Serial Communications

To learn how data is sent serially.

Serial Port Mode String

To learn about configuring serial port mode strings in Fernhill SCADA.

Serial Port Mode Editor

To learn about the editor that can edit serial port mode strings.