Returns the number of received characters available on a communications port. This function can be used to poll the COM port for data. The best way to receive characters on a COM port is to use the callback function that is set with OpenComPort or OpenComPortEx.
Parameter: port
Type: integer
Description: The port number of the
port to check or the resource number of the port to be checked if OpenComPortEx was used to open it.
Return value: number
Type: integer
Description: The number of characters available at the COM port.