Category Archives: SoMachine

Multiple IP Settings, Modicon M251 PLC remote connections and the InHand Networks IG601

The industrial automation world is increasingly connected. One of the projects this week involved a remote desktop session with a customer in the Midwest , from my NC location. The two of us were trying to log in to a PLC located in Alabama through a cloud based service.  This is when I realized the utility of the multi IP setting on gateway devices.

An increasing number of PLC, drives and HMI’s include Ethernet based protocols as standard. Many also allow program updates via the ethernet connection. This makes it easier to implement remote access solutions for troubleshooting and maintenance purposes. Set up the IP addresses for the control devices, use a gateway device from  eWon, InHand Networks  or Netbiter and you’re ready to go.

Cellular Remote Access devices- eWon Cosy 131, InHand Networks IG601 and Netbiter EC350.
Cellular Remote Access devices- eWon Cosy 131, InHand Networks IG601 and Netbiter EC350.


The Reason for Multiple IP Subnets on the Remote Network

Our PLC on this project was a Modicon M251. On this setup, for various reasons, the PLC program download for the M251 had to be through the Ethernet 1 port( M251 has two separate Ethernet networks embedded). The field devices connected to it ( drives, HMI) were on Ethernet 2. The customer wanted to retain access to the webservers of the field devices when they connected remotely. Occasionally they also needed to log in to the PLC and update the program.

So, in short, we had to connect to Ethernet 1 of the PLC but the gateway device had its IP settings set to the Ethernet 2 port.


To illustrate the setup:

Drives, HMI and PLC Ethernet network 2 located on the 192.168.3.xx subnet

PLC program download port on Ethernet network 1 located on 192.168.4.xx subnet

Remote PLC gateway
Two ethernet networks and a cellular gateway. PLC program was to be updated remotely via the cellular gateway device.


 Multi IP setting on IG601

This is where the InHand IG601 multiple IP LAN could be useful. Typically, the gateway device would need to set to the same IP subnet as the PLC, HMI or remote network. When there are multiple subnets in the remote network then the gateway device would have to be changed to access each of the subnets. The IG601 solves this as it can be set up with multiple IP addresses. Both M251 ethernet networks were set up with the corresponding gateway IP address on the IG601 as the gateway address:

Ethernet 1 at was set up to look at which was set up as one of the IP’s on the IG601.

Ethernet 2 at was set up to look at which was set up as the other IP on the IG601.

In the IG601 configuration, the multi-IP setting is easily setup in the Network>LAN settings.

Multi-IP LAN setting
Multi-IP setting page on the InHand IG601

The multi-IP feature was tested on my test setup and worked well.

Items to look out for during the M251/SoMachine and InHand IG601 setup

1. If the M251 IP address is altered, it may take a power cycle for it to take effect. If possible, set this up and test it before shipping the PLC or while onsite with it.


2. The gateway IP address needs to be set up on the M251 for both ports- Ethernet 2 and Ethernet 2. On this note, try to set and follow rules of setting the gateway IP address on your remote systems. Example : use for the gateway IP …etc.

SoMachine Ethernet gateway address
Gateway addresses are set for both networks.

3. The setup of the IG601 was covered in a previous post about connecting to a Modicon M241. Having done this twice before, I still slipped up with one setting on the IG601. That is to set the cellular Access Number to  *99***1# instead of leaving it blank. Not sure what this means  but the system registered on the AT&T network after that setting was made.

Remember to enter the access number as shown. It made a difference on my setup.
Remember to enter the access number as shown. It made a difference on my setup.


Hope this helps save a controls engineer some energy and potentially hours/days of travel time just to perform a  PLC program update or some troubleshooting. Thank you to the folks at InHand Network for their guidance on this back when I first set it up.

Amazingly, I went through this post without saying IoT or IIoT once. 🙂

Drop a line in the comments section below with questions or comments on this setup.


CODESYS Declaration Examples: Variables, Arrays, Function Blocks…


There are many ways to implement variable declaration in CODESYS. It can be easy to forget the syntax or specifics on some of them. This post covers them for reference. Also, a couple of programmer cautionary comics from XKCD at the bottom…    😀


CODESYS Variable declaration


Variable Declarations:

VarName : INT ;

Variable with located memory address

VarName AT % MW123: INT;


Variables with Initial Value:

VarName : INT := 23;

Variable initial values can be tied to another variable of the same data type:

VarName: INT:= VarName2;


VarName2:= INT;


Declaring STRING with defined length:

VarName2 :STRING(40);

With the above, a string of 40 characters is created. Each character is one byte.


Declaring STRING with initial assignment:



Declaring Arrays with Initial Value:

Array1: ARRAY[1..5] OF INT := [1,2,3,4,5];

Without initial value it would just be:

Array1: ARRAY[1..5] OF INT;

Some other notes about arrays:

The first element can be element zero, i.e.

Array1: ARRAY[0..5] OF INT;


Multi-dimensional Arrays:

Array1: ARRAY[0..5,0..2] OF INT;

Array1: ARRAY[0..5,0..2,0..4] OF INT;


Declaring Pointers:

PointerToStrArray : POINTER TO STRING ( 9 );

Declaring Pointers to Arrays:

PointerToStrArray : POINTER TO ARRAY[1..10] OF STRING ( 9 );

In both the pointer examples above, the pointer values can be loaded with the ADR function. More on that here.


Declaring Function Blocks with Inputs:

Declaring an OFF delay timer from the Standard library with an initialized preset time

OffDelayTimer: TOF:= (PT:=T#2S);

The above declaration method can also be used with the preset time tied to another variable of type time:

OffDelayTimer: TOF:= (PT: = PresetTime);

where the PresetTime is declared as follows:

PresetTime: TIME := T#2s;


One of the positive points of a textual variable declaration area is the option to copy and paste. In some programming environments, the alternate to a textual declaration is a tabular or table based variable declaration area. Some  table based ( or tabular) variable  areas might include a pull-down menu of options for each declaration. This may help someone who is beginning to learn in an environment.

Nevertheless, in the long term, textual declarations are more flexible. Another benefit is  opens up the option to generate the variable declaration externally- in Excel for example. The external declaration is useful for larger projects with multiple programmers. In Excel, a name can be created and multiple versions of a variable generated with prefixes or suffixes to that name. One example may be:

For a variable called SysRun:

The local variable could be SysRun_Local

The status to be fed to a SCADA system could be SysRun_SCADA

Instead of typing out: SysRun_Local: BOOL; and SysRun_SCADA: BOOL; , the entire declaration process can be automated in Excel and then copied and pasted into CODESYS.

To wrap up for now..

Comments in variable declaration field are important. It helps the next person who reads the code/program. It might even help you make sense of your work, in the future. Also, for function blocks, the comments on the same line as a variable become the description of input pins when the cursor hovers over a pin.


Include comments with variable declaration. Comments help refresh your memory or serve as a guide for the next user.
Include comments with variable declarations.Comments help refresh your memory or serve as a guide for the next user.


There are probably other useful points  and methods of variable declarations in CODESYS that are not included here. If one comes mind, please comment below.