This tells the driver to send some IOCTL data to DOS.

DevReq03Rec
Offset Size Contents
                                                                          
+0      1  bLen         14H (length of this request packet)
+1      1  bUnitNo      unit number
+2      1  bCmd         03H (command code)
+3      2  rStatus      OUTPUT: Device Status Word must fill before exit
+5H     8  res          (reserved)
+0dH     1  bData        (not used)
+0eH     4  pfBuffer     INPUT: buffer address
+12H     2  wLen         INPUT: size of data requested (in bytes)
OUTPUT: actual size of data being returned
20               size of this structure

rStatus  On exit, the driver must place a DevStatusWord here.  Always
set the Done bit (bit 8).  On an error, set the Done bit and
the Error bit (bit 15) and put a Device Error Code in the low
byte.

pfBuffer  is the address of a buffer in which the driver may place the
requested data.  You must not store more than wLen bytes here.

wLen  On entry, this specifies the size of the data DOS is
requesting, in bytes.

On exit, you must store the actual size of the data that you
supplied.

Notes:   The layout of the data in pfBuffer is entirely device-specific
and will vary from device to device.

  There is no way to specify just what type of data is requested.
See DvRq 13H (generic IOCTL) for a more flexible system.

  This is the device driver "catch-point" for DOS fns 4402H and
4404H (receive IOCTL data).

See Also: Device Requests
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Device Request 03H: IOCTL Input