Compatibility: 2.0+
Expects: AX    4406H
BX    file handle  (device or disk file)
Returns: AX    error code  if CF is set to CY
AL    input status code (if no error)
00H: End of file or device not ready
ffH: not EOF     or device ready
Info: This function checks to see if a device or file is ready for
input; i.e, has data waiting to be read.

If the handle is a disk file:
AL=00H file pointer has reached the end of file
AL=ffH file pointer is at EOF (next read will return 0 bytes)

If the handle is a device:
AL=00H the device is not ready (no input available)
AL=ffH the device is ready (input is available)

Notes:   This fn makes for a simple way to determine EOF or to see if a
device, such as a COM port, has any input to be read.

See Also: Fn 44H (IOCTL)
Fn 4407H (Query Handle Output Status)
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DOS Fn 4406H: IOCTL Query Handle Input Status