How to Configure Remote I/O with a Siemens PLC

Adding Network Coupler

– Click the Network Coupler icon

Enter IP Address

– Select the iR-ETN40R for this example
– Enter the IP address of the Network Coupler
– Click OK

The default IP address is 192.168.0.212

Automatic Scan

– Instead of entering the IP address, Automatic Scan can be used

Press Scan

– Click Scan

Scanning Complete

– The Network Coupler will populate along with the IP address
– A pop up indicating that the scanning is complete
– Click OK

Start Monitoring

– The Network Coupler is added into the project
– Click Start Monitoring to view online values

Monitor Started

– The Network Coupler is highlighted green when monitoring has started
– Monitor is started is displayed in the Log Message

Launch TIA Portal and Create a Project

– Open TIA Portal software.
– In Portal View, select Create new project.
– Enter: Project name, Storage location

This creates the project environment where all hardware configuration and programming will occur.

Add the S7-1200 PLC to the Project

– In Portal View, select Devices and Networks
– Navigate to: Controllers > SIMATIC S7-1200
– Choose the correct CPU model (1212C for this example)
– Select the firmware version matching the physical PLC.
– Click Add

The PLC will appear in the Device View hardware configuration

Device Configuration

– Double click Device Configuration
– Here you can see that the PLC was added to the Rack_0
– Save the project

Adding Ladder Diagram Logic Block

– Add a new block
– Name it Stop_Start for this example
– Select Function
– Language: LAD (Ladder Diagram) for this example
– Click OK to add it as a Program Block

Create PLC Tags

– Type the name of the tags under Name (Stop, Start, Motor)
– Change the data types to Bool

Editing PLC Addresses

– Address: Stop: 0.0, Start: 0.1, Motor: 0.2
– Change the operand identifier for Motor to Q, which is output

Think of it like this:
The first number (0) = which byte/word you’re looking at
The second number (0) = which bit inside that byte
So:
0.0 > byte 0, bit 0 (the very first bit)
0.1 > byte 0, bit 1
0.2 > byte 0, bit 2

Add Logic Blocks to a Rung

– Add two normally open contacts to the rung
– Simply drag the block to the rung

Adding Tags to Logic Blocks

– Add a tag to the logic block
– Click the question mark and drop down menu and select the tag

Tags added to Logic

– Add the remaining tags to the logic block

For more details on adding logic blocks to the rung, refer to the
Simatic TIA Portal Step 7 Basic V10.5 Getting Started Guide

Add Function to Main Logic

– Now you will need to add the Stop_Start Function to the Main [OB1] program block
– Open the Main [OB1] program block and click and drag the Stop_Start function onto the rung. This will add it.

In simple terms, the PLC only runs the logic that is inside the main program cycle.
In TIA Portal, the Main Block (usually OB1) is what the PLC actually executes every scan.

What happens if you don’t add the FB to OB1?
The PLC:
1. Runs OB1
2. Executes only the instructions inside OB1
3. Ignores any FBs or FCs that are not called
So even though the FB exists in the project, the PLC never runs it, so you won’t see its logic operating when online.

Function Added to Main Block

– The FB is now placed in the Main scan

PLC IP Address

– Right click on the ethernet port on the Siemens PLC GUI
– Navigate to the Ethernet Address tab
– Enter the IP address and Subnet mask of the S7-1200 PLC

The PLC and Remote will need to be on the same network and share the same subnet.

Add Modbus Configuration Program Block

– Add a new block
– Select Data Block
– Name it MBConfig
– Type: Global DB
– Click OK

Add Modbus TCP (Client) Instruction to Main Block

– Select the Main [OB1] Block
– Drop down the Communications Instruction
– Select Others folder
– Select MODBUS TCP
– Drag the MB_CLIENT Instruction intot the Main Block on the rung after the normally closed contact

Name the Call Option

– Call options with pop up when the instruction is placed in the main block
– Name it MB_CLIENT_DB (Modbus Client Data Block)
– Click OK

Assign Tags to the Instruction

– Now add the tags to the instruction
REQ = starts a Modbus request
DISCONNECT = tells the block to close the connection
MB_MODE = tells it what Modbus function to use
MB_DATA_ADDR = starting Modbus address in the server
MB_DATA_LEN = how many items to read or write
MB_DATA_PTR = where the PLC stores the data or gets data to send
CONNECT = server connection info
DONE = request finished OK
BUSY = still working
ERROR = request failed
STATUS = error/status code

Think of MB_CLIENT like this:
CONNECT = who to talk to
MB_MODE = what action to do
MB_DATA_ADDR = where in the server to start
MB_DATA_LEN = how much data
MB_DATA_PTR = where your PLC stores it
REQ = go do it
DONE / ERROR / STATUS = tell me what happened

To see more details on this instruction and its usage please refer to the Simatic S7 S7-1200 Programmable Control Manual – Communication processor and Modbus TCP

Remote I/O Modbus Parameters

– Check to make sure the modbus parameters is set to Modbus TCP in EasyRemote IO

Remote I/O Address Map

– Select the Address Map
– Built-in “I” (the channels being used)
– Look at Channels 0-2 modbus addresses
Channel 0 is 0x_0, Channel 1 is 0x_1 and Channel 2 is 0x_2

Think of it as:
address group = digital bit area
0 = the first bit
So 0x_0 is basically the first digital point.

In TIA Portal
If you want to communicate with that bit through MB_CLIENT, you would typically set:
MB_DATA_ADDR := 0
MB_DATA_LEN := 1
MB_MODE based on what it is:
read discrete input for an input
read coil / write coil for an output
MB_DATA_PTR points to where the result will be stored in your PLC memory

Modbus Client Instruction with Tags

Here is what the instruction will look like with the tags assigned

Again for more details use the Simatic S7 S7-1200 Programmable Control Manual

Compile the PLC Project for Hardware

– Right click on PLC 1 [CPU 1212C…]
– Select Compile
– Select Hardware (rebuild all)
– Hardware will be compiled

Compiling the hardware configuration makes sure:
– The PLC knows what modules are installed
– I/O addresses are assigned correctly
– The rack and network setup match the real PLC

For example, it tells the PLC things like:
Slot 1 = CPU
Slot 2 = digital input module
Slot 3 = digital output module

Compile the PLC Project for Software

– Right click again on PLC 1 [CPU 1212C…]
– Select Compile
– Select Software (rebuild all)

Compiling the software checks and prepares your program:
– Checks for errors in logic
– Makes sure tags and addresses are correct
– Converts ladder/FBD into PLC machine code
Without compiling, the PLC may not accept the program or it might contain errors.

Project Compiled

– Compiling finished with no errors or warnings

Download to PLC

– Right click again on PLC 1 [CPU 1212C…]
– Select Download to device
– Select Hardware and software (only changes)

Download Preview

– The Load Preview window will pop up
– Click Load to begin downloading

Download Completed

– a Load results window will pop up indicating that Downloading to device completed without error
– Click Finish

Save Project and Go Online

– Save the project
– Click Go online

PLC Online

– In the Project tree, the PLC, Program Blocks, PLC tags and Local modules have a green check mark or circle indicating that everything was downloaded to the PLC successfully

Monitor the PLC Project

– The last step is to monitor the online project
– Select the Monitoring on/off button to monitor the PLC values in the logic block