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Standard coils, discrete inputs, and registers with UINT16, INT16, UINT32, INT32 and FLOAT32 operations are supported. See additional details in the Configuration and Connections sections below.
Supported Features
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Standard registers:
Coils: Available as a model output, a model input (controlled by the master) or both
Discrete inputs: Available as a model output
Input registers: Available as a model output. The supported data types are UINT16, INT16, UINT32, INT32 and FLOAT32
Holding registers: Available as a model output, a model input (controlled by the master) or both. The supported data types are UINT16, INT16, UINT32, INT32 and FLOAT32
Supports TCP and RTU modes
Allows multiple-slave instantiation
Configurable TCP port when operating over TCP mode
Configurable serial port parameters when operating over RTU mode
Supports reconnection with the master device(s) if a connection is lost
TCP mode supports connecting multiple masters to the same slave
TCP mode supports having multiple slaves with the same IP address and TCP port combination; in this scenario, the slave ID is used as the differentiator
Configuration
The driver is entirely configurable via the RT-LAB interface. Users can add, delete, and duplicate Modbus slave devices. Configuring holding registers, input registers, discrete input or coils is also an easy task.
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Mode | Select "TCP" or "RTU" depending on how the Modbus slave device is configured to communicate. | |
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Slave ID | ID of the Modbus slave. Each slave must be configured with a unique identification number. This is due to the fact that:
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TCP specific parameters |
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RTU specific parameters | Modbus ID: ID of the Modbus slave. In RTU mode, many slaves can be connected on the same physical serial link. Because of that, each Modbus slave must be configured with a unique identification number.
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Cycle output ratio rate (ms) | Defines the rate (in milliseconds) at which the data from the model is written in the slave's outputs (coils and holding registers). When the slave's outputs are controlled from the model and from the master, this parameter must be set to a value greater than the time step of the model. Otherwise, the write operations made by the master will never be reflected in the model. | |
Byte Order | Defines how 32 bits data is encoded. Any of the byte ordering cases are possible (ABCD, BADC, CDAB, DCBA). ABCD refers to the network byte order. | |
Permit read/write requests with address gaps | From the lowest address to the highest address configured, this option creates dynamically new coils, discrete inputs, holding registers and input registers at every address that is not defined by the user and assigns a value of 0. |
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Once the driver has been configured as desired and associated with the proper model subsystem, the user will have to connect points in the model to points in the driver by using the designated RT-LAB GUI. This connection panel will show all the driver's and model's connectable points, once the model has been compiled. It is also possible to make connections to LabVIEW Dashboards panels.
The example model provided with RT-LAB is already packaged with connections between the driver and the model. It can be used as an example to understand how the connections between the model and the driver should be done.
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In TCP mode, an additional "Connected" connection point is available and can be used in the model to indicate if the Modbus slave is connected to a Modbus master or not. It represents the number of Modbus masters currently connected to the Modbus slave. This value will be the same for all slaves sharing an IP address and TCP port combination.
In RTU mode, an additional "Bus Activity" connection point is available and can be used in the model to indicate if the Modbus slave is receiving requests from a Modbus master.
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