The IOCTL_SERIAL_IMMEDIATE_CHAR request causes a specified character to be transmitted as soon as possible. The immediate character request completes immediately after any other write that might be in progress. Only one immediate character request can be pending at a time.

Major code


Input buffer

The AssociatedIrp.SystemBuffer member points to the UCHAR value to transmit immediately.

Input buffer length

The Parameters.DeviceIoControl.InputBufferLength member is set to the size, in bytes, of a UCHAR.

Output buffer


Output buffer length


Status block

If the request is successful, the Information member is set to the size, in bytes, of a UCHAR. Otherwise, Information 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 a previous immediate character request is pending.


Requirement Value
Header ntddser.h (include Ntddser.h)