IOCTL_SERIAL_GET_MODEMSTATUS control code
The IOCTL_SERIAL_GET_MODEMSTATUS request updates the modem status, and returns the value of the modem status register before the update.
For more information, see the definitions of the modem status register bits (SERIAL_MSR_DCTS through SERIAL_MSR_DCD) in the Serial.h header file in the Serial driver sample on GitHub.
The Parameters.DeviceIoControl.OutputBufferLength member is set to the size, in bytes, of a ULONG.
The AssociatedIrp.SystemBuffer member points to a client-allocated ULONG buffer that the serial controller driver uses to output the value of the modem status register.
If the request is successful, the Information member is set to the size, in bytes, of a ULONG. Otherwise, the Information member is set to zero.
The Status member is set to one of the Generic Status Values for Serial Device Control Requests.