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Registry Settings for a Legacy COM Port

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In older versions of Windows, a named serial COM port located on the case of a PC, the inbox Serial.sys and Serenum.sys drivers were used.

Note

This topic describes programming traditional COM ports. For information on USB attached serial ports, see USB serial driver (Usbser.sys).

This topic describes the registry settings that Serial uses with legacy COM ports. Serial always configures a legacy serial device as a COM port.

Serial queries these entry values when it enumerates a legacy COM port. If a device-specific entry value is not present, Serial uses a Serial service value.

The registry settings for a legacy COM port are under a corresponding legacy COM port subkey that is under the ..\Services\Serial\Parameters key.

For general information on how to locate and work with Windows drivers registry keys, see Registry Trees for Devices and Drivers.

The following entry values are the same as described for a Plug and Play serial device:

  • ClockRate

  • PortIndex

  • Indexed

  • RxFIFO

  • TxFIFO

  • MaskInverted

  • DisablePort

  • ForceFifoEnable

The following additional entry values are used with legacy COM ports:

PortAddress (REG_DWORD)
Specifies the untranslated base I/O address for the COM port control registers. Serial reads this value. The value cannot be zero. The default value of PortAddress is 0x00000000.

Interrupt (REG_DWORD)
Specifies the untranslated interrupt vector, as appropriate for the bus type. Serial reads this value. The value cannot be zero. The default value of Interrupt is 0x00000000.

DosDevices (REG_SZ)
Specifies the name of the COM port. The name of a COM port is typically COM<n>, where <n> is a COM port number that the installer obtains from the COM port database. However, a COM port name can be set to any non-NULL string. Serial uses the port name to create a symbolic link to the COM port that is visible in usermode. The default value of DosDevices is a NULL string.

InterruptStatus (REG_DWORD)
Specifies the raw I/O address for the interrupt status register. Serial reads this value. The value is omitted if the port is a stand-alone port. The value cannot be zero if the port is on a multiport device. The default value of InterruptStatus is 0x00000000.

BusNumber (REG_DWORD)
Specifies the system-wide bus number for the bus type. Serial reads this value. The default value of BusNumber is 0x00000000.

BusType (REG_DWORD)
Specifies the bus type. Serial reads this value. The default value of BusType is determined by Serial during driver initialization.

InterruptMode (REG_DWORD)
Specifies the interrupt mode. Serial reads this value. The default value of InterruptMode is CM_RESOURCE_INTERRUPT_LATCHED.

InterruptLevel (REG_DWORD)
Specifies a raw interrupt level value that is appropriate for the bus type. Serial reads this value. The default value of InterruptLevel is 0x00000000.

PnPDeviceID (REG_SZ)
Specifies a Plug and Play device identifier for a Plug and Play device. Serial reads this value. The default value of PnPDeviceID is a NULL string.

LegacyDiscovered (REG_DWORD)
Boolean flag that indicates whether Serial has previously reported the device to the Plug and Play manager. Serial reads and sets this value. If LegacyDiscovered is nonzero, Serial has previously reported the device and does not report the device again. Otherwise, Serial reports the device and sets the entry value to 0x00000001.