Port drivers use port driver services to initialize and block access to hardware. A port driver calls the _VCOMM_Register_Port_Driver service when it is loaded. A port driver calls the _VCOMM_Add_Port service once for each port it supports.
The _VCOMM_Acquire_Port and _VCOMM_Release_Port services enable port drivers to acquire and release exclusive access to communications devices. A port driver should acquire a port when its PortOpen function is called, and release a port when its PortClose function is called. Other VxDs that access communications hardware directly should also call these services.
VCOMM relies on the virtual communications device (VCD) to block access to communications devices. The _VCOMM_Acquire_Port service has no effect when used with communications resources that VCD does not support, although the service still returns a handle in such cases.
See also _VCOMM_Acquire_Port, _VCOMM_Add_Port, _VCOMM_Register_Port_Driver, _VCOMM_Release_Port