IOCTL_SERIAL_SET_DTR control code
The IOCTL_SERIAL_SET_DTR request sets DTR (data terminal ready).
If the handshake flow control of the device is configured to automatically use DTR, a client cannot clear or set DTR.
To clear DTR, a client can use an IOCTL_SERIAL_CLR_DTR request.
The Information member is set to zero.
The Status member is set to one of the Generic Status Values for Serial Device Control Requests. A status of STATUS_INVALID_PARAMETER indicates that the handshake flow control of the device is set to automatically use DTR.