Modbus Read

This function block reads data from a Modbus server (coils or registers) using a provided Modbus client connection. Use the on-screen controls to select the target address, the number of values to read, and the Modbus data type.

📥 Inputs

Enable A boolean gate to allow or prevent reading. When False the block will not perform a read and returns no data.

Modbus Client Provide a Modbus client connection object (usually coming from a Modbus Connect block). The block uses this client to communicate with the server.

📤 Outputs

Data The read result as a generic list. For register reads this is a list of numeric register values; for coil/discrete reads this is a list of boolean values. If reading fails or is disabled, output is empty/None.

🕹️ Controls

Address Enter the start address (integer) on the Modbus device to read from.

Quantity Enter how many consecutive items (registers or coils) to read.

Data Type Choose the Modbus data type to read: Coil, Discrete Input, Input Register, or Holding Register.

🎯 Features

• Supports reading both bit-based (coils/discrete inputs) and word-based (input/holding registers) data types.

• Uses an external Modbus client connection provided to the Modbus Client input, keeping communication separate from the block’s settings.

• Simple numeric and boolean results are returned as a list suitable for logging, plotting, or downstream processing.

• Built-in error reporting surfaces communication failures so you can react (reconnect, retry, alert).

⚙️ Running mechanism

When active, the block checks the Enable input and requires a valid client on the Modbus Client input. It reads the configured address range using the selected Data Type and returns the values on the Data output. If the read fails or the block is disabled, it returns no data and logs a helpful error message.

💡 Tips and Tricks

• Use Modbus Connect to create and provide the required Modbus Client connection.

• Use Logic Input or Rising Edge to control when reads happen (manual trigger or single-shot reads).

• To write values back to a device, combine with the Modbus Write block.

• Log readings for later review using CSV Export or persist them with Data Write Local / Data Write Global.

• Visualize numeric outputs in real time by feeding numeric results into the Scope block.

• Use Debug Input to inspect and verify the returned Data during setup and troubleshooting.

🛠️ Troubleshooting

• No data returned: ensure a valid client is connected to the Modbus Client input and Enable is True.

• Wrong values or partial reads: check Address and Quantity are within the device’s address map and within device limits.

• Communication errors: verify network/serial settings via the Modbus Connect block and ensure no other application is blocking access.

• Unexpected data format: confirm you selected the correct Data Type (coils vs registers) for the values you expect.