!"
A device setup GUID identifies devices that have similar capabilities and are
installed and configured in the same way. Devices that have the same device
setup GUID use the same class installer to assign drivers. COM-port devices are
in the Ports class. The class??™s GUID is GUID_DEVCLASS_PORTS defined in
devguid.h in the WDK. The class also includes parallel (LPT) ports.
COM-port devices in the Ports class must support the software interface
defined in ntddser.h in the WDK. The file defines functions compatible with
the 16550 UART chip used in many early serial ports. Devices aren??™t required
to implement the 16550??™s asynchronous serial interface, however. For example,
a USB virtual COM port in the Ports class might have a parallel or other interface.
Some intelligent multiport serial cards instead use the MultiportSerial device
setup class (GUID_DEVCLASS_MULTIPORTSERIAL).
Chapter 3
40
" !"
A device interface GUID identifies devices that applications can access in the
same way. During device installation, a driver registers the device as an instance
of a device interface class and associates a symbolic link name with the device.
The device interface GUID used by internal serial port s i s
GUID_DEVINTERFACE_COMPORT defined in ntddser.h. (Some older
software uses GUID_CLASS_COMPORT instead.) The symbolic link name
has the form COM
, where n is a unique number.
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