Post submitted by  Paul Puttick 

  of  Tethco Technologies

 www.tethco.com

This post explains how to configure a Micrologix 1000 serial port to a Modbus serial slave, to a Modbus TCP/IP.

Materials

Micrologix 1100

Moxa MGate MB-3180

Cable

Male 8 pin mini-din to Micrologix.  Female DB9 to Moxa Mgate serial Connection.  Using RS-232.

Pinout:

Male 8 pin Mini-Din                    Female DB9

                2—————GND—————5

                4<<<<RxD<<<<<<TxD<<<<<<3

                7>>>>TxD>>>>>>RxD>>>>>>2

                6—————CTS—————- 8

                3—————RTS—————- 7

Micrologix Serial Port Configuration

Select Channel Configuration, then Channel 0.  Driver = Modbus RTU Slave.  Node Address = 1(can be any unique address from 1-247) Baud Rate = 9600.  Parity = Odd.

Protocol Control using no Handshaking.  InterChar. Timeout = 2ms.  Pre Transmit Delay = 2ms.

Configure the desired Modbus data tables.   Enter a number for the desired data Files in the fields for Coils(00001), Contacts(10000), Input Registers(30001), Holding Registers(40001).  For example, I used 50 for Holding Registers field.  Data file N50 is created automatically.  Select N50 enter a description and adjust the data file elements to suit.  N50:0 = Modbus register 40001.

Moxa Mgate MB-3180 Configuration

Install MGate Manager using the provided CD.  Initially the MGate has a default IP.  Configure the LAN on your computer to be in the same subnet as the MGate default IP.  Connect to the device, open MGate Manager, then select Broadcast search.  Highlight the device, select “Configuration”. 

Under the mode tab select RTU Slave Mode.

Select the Serial tab.  Configure Port 1 as Follows:  Baud Rate = 9600, Flow Control = None, Party = Odd, FIFO = Disable, Start Bit = 1, Interface = RS232.

Select the Modbus tab.  Initial Delay = 2ms.  Modbus TCP Exception = Disabled.  Port 1 Response Time-Out = 1000ms. 

You can use the Auto Detection button to test your connection.  If you see a response on the Node Address 1 then connection is ok. 

Testing

To test I used some free demo software.  Modscan32.   To connect select Connection.  Connect Using – Remote Modbus TCP Server.  Enter the IP of the Moxa MGate.  Select Protocol Selection pushbutton.  Transmission Mode = RTU.  Slave Response Timeout = 1000ms.  Delay Between Polls = 2ms.  Select Ok.  Device ID = 1(needs to match PLC Node address).   

Modscan32 is a Windows shareware program designed to act as a Modbus Master.  It is a simple way to read or write data to the connected slave device using RTU or ASCII.  The weblink below is a 30 day evaluation.  Data collection will cease at approximately 3 1/2 minutes after receiving the first valid slave response. 

  ModScan32.zip (851K)

Updated to Version 7.B01
(Feb 27, 2009)

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