Example: Exposing the Blink Project's LED Output

This walk-through configures an S7Comm server against the standard Autonomy Edge blink project and connects to it from a generic S7 client. By the end you will have a Siemens-style DB1 that toggles every cycle as the program runs, observable from any S7 tool.

The starting project is the default blink program: a single rung that toggles a BOOL output named led mapped to %QX0.0, driven by two timers. Nothing about the program logic needs to change.

Step 1: Add an S7Comm Server

1. In the project explorer, click the + button.
2. Choose Server, then select Siemens S7comm as the protocol.
3. Name the server blink-s7-server and click Create.
4. The new entry appears under the Servers folder. Click it to open the configuration panel.

Step 2: Configure the Server

In the Server Configuration accordion, set:

That is everything you need on the network side. The defaults are correct for a standard Siemens client.

Step 3: Define DB1

The blink project's only output is led at %QX0.0. This is bit 0 of byte 0 of the Boolean Output buffer, so the matching mapping type is Boolean Output (%QX).

1. Expand the Data Blocks accordion.
2. Click + Add Data Block.
3. Fill in:

1. Click Add Data Block.

The accordion now shows a single row: DB1 / Blink LED state / 1 bytes / Boolean Output (%QX). The header counter reads Data Blocks (1/64).

The combination of Size = 1 byte, Start Buffer = 0, and Bit Addressing = on exposes the 8 bits of %QX0.0 through %QX0.7 as DB1.DBX0.0 through DB1.DBX0.7. Only DB1.DBX0.0 is wired to anything in this project. That is the blink LED.

Step 4: Save and Transfer

Save the project and transfer it to a vPLC device the same way you would any other project. The runtime starts the S7Comm listener on port 102 as soon as the program runs.

Step 5: Connect from an S7 Client

The plugin is server-side; the rest of this section describes things you do on the client tool. Pick whichever tool is convenient:

• python-snap7: a Python wrapper around the Snap7 library
• libnodave / NodeS7: Node.js drivers used by many open-source SCADA stacks
• A Siemens HMI (WinCC, TIA Portal monitor windows)
• Diagnostic GUIs such as PLCSIM Advanced's connection tester

S7 clients typically ask for four things to make a connection:

Rack and Slot are S7 connection conventions on the client side. They do not correspond to anything you configure in the Autonomy Edge editor. The OpenPLC runtime is not a real S7 chassis.

In informal documentation the endpoint is sometimes written as s7://192.168.1.50:102. The S7 protocol does not define a URI scheme, but the shorthand is convenient.

Step 6: Read the Toggling Bit

Once connected, ask the client to read DB1.DBX0.0. With the blink program running, the value alternates between false and true roughly every 500 ms / 1500 ms (driven by the project's TON and TOF blocks).

Here is what a minimal python-snap7 reader looks like, for reference (this is client-side code, not something you put in the project):

python
import snap7

client = snap7.client.Client()
client.connect('192.168.1.50', 0, 1)        # IP, rack, slot
data = client.db_read(1, 0, 1)              # DB1, offset 0, 1 byte
bit = bool(data[0] & 0x01)                  # DBX0.0 is the LSB of byte 0
print('LED state:', bit)
client.disconnect()

You will see the bit flip on every read as the rung evaluates.

Step 7: Add a Writable DB (Optional)

If you also want the client to be able to write values that the PLC program can react to, add a second DB pointing at a Boolean Memory (%MX) or Word Memory (%MW) area, and reference the corresponding %MX / %MW variable from your ladder. Memory mappings give you read-write semantics that don't compete with the PLC scan over the output buffer.

What's Next?

• Troubleshooting: Resolve common connection failures
• Data Blocks: Browse the full mapping catalog for more elaborate setups
• S7Comm Server Overview: Return to the protocol overview