> For the complete documentation index, see [llms.txt](https://captic-2.gitbook.io/docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://captic-2.gitbook.io/docs/overview/hands-on/integrating-your-robot/integration-flow/protocols/modbus.md).

# Modbus

Connect to Modbus TCP and Modbus serial devices.

The Integration Flow includes Modbus nodes for **Modbus TCP** and **Modbus serial**. Use them to read and write registers and coils on PLCs and other devices that speak Modbus. You'll find them under **modbus** in the palette.

## Connect

1. Add a Modbus client configuration with the device's IP address, port (usually `502`) and unit ID.
2. Use the read and write nodes to exchange registers and coils.

For node details, see the [upstream documentation](https://flows.nodered.org/node/node-red-contrib-modbus).

## Data layout

We recommend the [PLC data layout](/docs/overview/hands-on/integrating-your-robot/integration-flow/plcs.md), created as holding registers.

{% hint style="info" %}
Doosan robots are read over Modbus with a dedicated node. See [Doosan](/docs/overview/hands-on/integrating-your-robot/integration-flow/robots/doosan.md).
{% endhint %}