Serial Receive

Read data from UART port

  • Library:
  • Simulink Coder Support Package for NXP FRDM-K64F Board

Description

The Serial Receive block reads data from the Universal Asynchronous Receiver Transmitter (UART) port on the board.

To select the UART port, use the UART parameter.

The block reads the values from the UART port, using the Rx (receiving) pin on the port. To specify the Rx pin, go to Configuration Parameters > Hardware Implementation pane > UARTx > Rx Pin.

During the external mode simulation, the block outputs the results from the executable running on the target hardware.

During simulation in all other modes, the block outputs zeroes.

You can choose to read data in blocking or non-blocking mode.

Ports

Output

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At each sample time, the Rx port outputs the values read from the UART port using the Rx pin on the port. To specify the Rx pin, go to Configuration Parameters > Hardware Implementation pane > UARTx > Rx Pin.

The port outputs a data vector of the size that you specify in the Data length (N) parameter. For more information, see Receive data from UART port.

Data Types: int8 | uint8 | int16 | uint16 | int32 | uint32 | single | double

When you select the Output status parameter, the Status port becomes available. The port outputs 0 when the length of data received is greater than or equal to the length specified in the Data length (N) parameter. A value of 0 indicates a successful read operation.

Otherwise, it outputs 32, indicating that no new data is available.

Dependencies

You can choose to display the status of the read operation only in the non-blocking mode. To enable the non-blocking mode, clear the Wait until data received parameter, and then select the Output status parameter.

Data Types: uint8

Parameters

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Select the UART port on the board from which the block reads data. At each sample time, the Rx port on the block outputs the values read from the UART port using the Rx pin on the port. To specify the Rx pin, go to Configuration Parameters > Hardware Implementation pane > UARTx > Rx Pin.

Select the data type in which the block receives data from the UART port.

Specify the length of data that you want to receive at each sample time.

  • on — When you select this parameter, the read operation runs in the Blocking mode. The read operation is blocked while waiting for the requested data to be available. If data is available, the Rx port outputs data. If data is not available, the Rx port waits for data. The Status port is hidden.

    A task overrun occurs if the target hardware is still waiting for the data to be available when the next read operation is scheduled to begin.

    To fix overruns:

    • Increase the time step by using the Sample time parameter.

    • Reduce the length of data requested by using the Data length (N) parameter.

  • off — When you clear this parameter, the read operation runs in the Non-blocking mode. When reading data, if data is not available, the Rx port outputs zeroes. The Status port outputs 32, indicating that no new data is available.

When you select this parameter, the Status port becomes available.

The port outputs 0 when the length of data received is greater than or equal to the length that you specify in the Data length (N) parameter. A value of 0 indicates a successful read operation.

Otherwise, it outputs 32, indicating that no new data is available.

Dependencies

You can choose to display the status of the read operation only in the non-blocking mode. To enable the non-blocking mode, clear the Wait until data received parameter, and then select the Output status parameter.

Specify how often the block reads data from the UART port. When you specify this parameter as-1, Simulink® determines the best sample time for the block based on the block context within the model.

Receive data from UART port

This section explains the values at the output port, with the following block parameters specified as:

Block ParameterValue
Data typeuint8
Data length (N)4

The value at the output port vary depending on whether the length of data received is less than, greater than, or equal to the length of requested data.

  • Length of data received = Data length (N): The Rx port outputs a data vector of the size specified in the Data length (N) parameter.

    Suppose that the Data length (N) parameter specified is 4 and the length of data received is also 4.

    In this case, the port outputs a data vector of size 4 filled with the bytes from the received data.

  • Length of data received < Data length (N): The Rx port outputs a data vector of the size specified in the Data length (N) parameter filled with zeroes.

    Suppose that the Data length (N) parameter specified is 4 and the length of data received is 3 bytes.

    In blocking mode, the read operation is blocked while waiting for the fourth byte to be available.

    In non-blocking mode, the port outputs a data vector of size 4. All the spaces in the vector are filled with zeroes.

  • Length of data received > Data length (N): The Rx port outputs a data vector of the size specified in the Data length (N) parameter. The vector contains only the first N bytes from the received data. The remaining data bytes are dropped.

    Suppose that the Data length (N) parameter specified is 4 and the length of data received is 5 bytes. In this case, the port outputs a data vector of size 4. The vector contains only the first 4 bytes from the received data. The remaining data byte is dropped.