Create a connection to a serial port device.

device = serialport("COM3",9600)

device = 

  Serialport with properties:

                 Port: "COM3"
             BaudRate: 9600
    NumBytesAvailable: 0

  Show all properties, functions

Write some data to the device and view the number of bytes available to be read in the input buffer.

write(device,1:5,"uint8")
device.NumBytesAvailable

ans =

     5

Flush both the input and output buffers.

flush(device);

View the number of bytes available to be read.

device.NumBytesAvailable

ans =

     0

The input buffer has no data.