To open the port, VCOMM calls the PortOpen function for the port driver that best supports the device. If successful, the PortOpen function returns the address of a _PORTINFORMATION structure. This address is used to identify the open port in all subsequent calls to port driver functions. The first field of the _PORTINFORMATION structure must be a _PORTDATA structure, but additional fields can be defined by the port driver. The _PORTDATA structure contains information about an open communications device that is used by VCOMM, the port driver, or both. It includes a pointer to the port driver's _PORTFUNCTIONS structure, that contains the addresses of all the port driver functions except Enumerator, Inquire, and PortOpen.
To close a communications port, VCOMM calls the port driver's PortClose function.
PortClose, _PORTDATA, _PORTFUNCTIONS, _PORTINFORMATION, PortOpen