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v10.0.1.x for R2026a
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Modbus - Client Receive

Modbus - Client Receive — Sends read requests to the remote Modbus RTU server and outputs the received data.

Library

Simulink Real-Time - Speedgoat

Description

This block is used to receive data from the remote Modbus RTU Server. You can use multiple Modbus RTU Client Receive blocks for each Modbus RTU client node configured in your model.

Ports

Inputs
ENA

Boolean input to allow the user to manage the handling of Modbus requests to the defined Modbus Server. This input is only active if the Manage Requests checkbox is enabled. Send a boolean value of 1 to enable sending or 0 to disable the sending of Modbus requests. If the sending is stopped, the Receive block will still be able to receive data and update its output port.

Outputs
RX

Array of length Quantity that includes the values received from the Modbus Server for the data range specified by the Index and Quantity parameters. The data type depends on the selected function code.

  • For Coils and Discrete Inputs, the output port is a vector of the BOOLEAN data type, where the length of the vector is defined by the Quantity parameter. Each BOOLEAN element of the vector represents one bit.

  • For Holding Registers and Input Registers, the output port is a vector of the UINT16 data type, where the length of the vector is defined by the Quantity parameter. Each UINT16 element of the vector represents one word/register.

Use Byte Unpack blocks to convert to signed values or floating-point numbers. You can unpack a vector of type UINT16 and length 4 to one double value.

Parameters

Client Interface ID

Apply the Client Interface ID of the corresponding Setup block. Must range between 0 and 65535.

Remote Server Node ID

Enter the Node ID of the remote Modbus RTU server. You can use multiple Receive blocks to exchange data with that server. Must range between 0 and 247. Setting the Node ID to 0 will address all Modbus RTU servers on the serial line!

According to the Modbus standard, Node ID 255 means NON-SIGNIFICANT. When addressing a Speedgoat Modbus Server and the node identifier is set to 255 but Node 255 is not configured in the server itself, the requested command is performed on the first node specified in the server configuration.

Function Code

Select the Modbus Function Code you want to use for your communication. The options are:

  • FC1 (Read Multiple Coils)

    The output will be an array of booleans.

  • FC2 (Read Multiple Discrete Inputs)

    The output will be an array of booleans.

  • FC3 (Read Multiple Holding Registers)

    The output will be an array of uint16.

  • FC4 (Read Multiple Input Registers)

    The output will be an array of uint16.

Refer to the Modbus usage notes for further information about function codes.

Data Index

The first index of the data range you want to send or receive. Must range between 0 and 65535.

  • For Coils and Discrete Inputs, the parameter defines the start bit.

  • For Holding Registers and Input Registers, the value defines the start word.

Data Quantity

The length of the data range you want to send or receive. Index + Quantity must not exceed 65536.

Swap Bytes

The bytes of a register must be swapped if the sender and the receiver interpret the byte order in different ways (endianness). The Speedgoat real-time target machine uses little-endian, while some clients use big-endian. If the swap option is enabled, all register values from the application context will be swapped before they are sent to the network. All register values received from the network will be swapped before they are submitted to the application context. The swap option only affects input registers and holding registers (transmitted by function codes FC3, FC4, FC5, FC6, FC16). Discrete inputs and coils are not affected. Use Byte Reversal blocks instead of enabling the global byte swapping if only single registers need to be swapped.

Polling Interval

The polling Interval is the time interval between sending Modbus requests to the server. Must range between 0 and 7,200,000 milliseconds, which corresponds to a maximum of 2 hours.

Manage Requests

Tick this checkbox if you want to control sending Modbus requests. This activates the ENA input port of the Receive block. If the sending is stopped, the Receive will still be able to receive data and update its output port.

Sample Time

Defines the base sample time at which this driver block gets its sample hit. This parameter can also be set to -1 for inherited sample time. The units are in seconds.