Get Allen-Bradley and Rockwell Automation data to MQTT and the cloud.
If your Logix or Micro800 can serve Modbus, an AppBlocks gateway polls its registers, scales the values, and publishes them to any MQTT broker, an HTTP API, Azure IoT, or AppBlocks Cloud. The gateway is a separate device next to the controller, and its logic is a flowchart your whole team can read.
One mapping on the PLC, then the gateway does the rest.
A one-time Modbus mapping
You decide which values the PLC exposes as Modbus registers. Everything else in the program stays as it is.
Read-only unless you say so
The gateway only reads. If you choose to send setpoints back, limits are checked in the flow before anything reaches the PLC.
Secure on the way out
MQTT over TLS with QoS 0, 1, or 2, and HTTPS for API calls, so plant-side Modbus never leaves the plant.
Two steps from register map to broker.
The flow uses real block names. Open the Designer and you’ll find each one in the palette.
Step 1: Serve Modbus from the Allen-Bradley controller
ControlLogix and CompactLogix controllers talk EtherNet/IP and don’t include a Modbus TCP server out of the box. The usual ways to add one are Modbus server add-on instructions in the controller program, a communication module from a third party, or a Modbus protocol converter next to the panel.
Micro800 controllers can speak Modbus RTU on their serial port, which suits an RS-485 gateway.
- Pick the Modbus path that fits your controller and your standards
- Expose only the tags you choose, as holding registers
- The controller program stays in charge; the gateway reads
Controller tag Modbus address Gateway variable Tank1_Level 40001 tank_level Pump1_Running 40002 pump_running Line2_Speed 40003 line_speed
Step 2: Poll the registers and publish
A timer sends a Modbus Request. When the PLC answers, On Modbus Response scales the value and publishes it. If the PLC stops answering, On Modbus Timeout publishes a status topic, so your dashboard can tell zero from offline.
- Function codes 01–06, 15, and 16
- Fast tags every second, slow ones every minute
- Report by exception to save cellular data
Build your first gateway in an afternoon.
Allen-Bradley and Rockwell Automation and the other product names on this page are trademarks of their owners. AppBlocks is not affiliated with or endorsed by them.
Questions, answered.
Can AppBlocks read EtherNet/IP tags directly?
Not today. AppBlocks talks Modbus, so a Logix controller needs a Modbus path first, as described above.
Which Allen-Bradley controllers are the easiest to connect?
Controllers that already speak Modbus are simplest, such as Micro800 controllers on a serial port. For Logix controllers, ask your Rockwell reseller about the Modbus options for your model, or use a protocol converter.
Is Modbus TCP secure?
Modbus has no authentication or encryption of its own, so keep the PLC-to-gateway link on the plant network. The gateway then publishes outward over MQTT with TLS or over HTTPS.
What hardware do I use for the gateway?
A Tibbo Project System device with an Ethernet port and an RS-485 module is the usual choice, in a DIN-rail enclosure. Add a 4G LTE module for sites without a network. AppBlocks also runs on Zephyr boards such as the ESP32. Supported boards.
Ready to connect your first device?
Start free in your browser, follow the tutorials, or book a free one-on-one session. No board yet? We’ll demonstrate everything on ours.