DEVICE DISCRIPTOR:

The device descriptor notifies the device driver information necessary
for operation. It describes the physical address interrupt level and
vector used for interrupts.
A structure pointed to by a symbol named 'Devcon' contains video mode,
mouse,keyboard and serial port information. This structure is used by
the driver to initialize the graphics board in the desired state when
the driver is first called (or iniz'ed).

This structure is four long words declared at the bottom of the device
descriptor. (See the '.a' file in this directory).
An include file "rgdefs.d" contains defines for the various bits for
each field.


The 1st long word is used as an enable mask. To modify any of the other
fields, the appropriate bit in this field must be set.

The 2nd long word sets the video resolution/mode. Set the desired mode
in this word and set the VIDEO_ENABLE bit in the enable mask (1st long word)
to change the video mode.

The 3rd long word is a composite field. Bits in this field control the
keyboard,mouse and serial port devices. To turn a device on the appropriate
bit must be set in this word and the enable bit for the device must be
set in the 1st long word (enable_mask). If the bit is clear (0) and the
enable bit is set in the enable_mask, the device will be turned OFF.
If the graphics board used does not support these devices writting this
field will have no effect.


MOUSE/SERIAL: (for boards with a serial port)
There exits only one serial port on the graphics board. It may be used for
either the mouse or the serial port. The mouse will take precident over 
the serial port (if both are enabled only the driver will expect mouse data).

KEYBOARD: (for boards that support a keyboard connected to the graphics board)
The keyboard is polled by the graphics board. Only enable the keyboard if
your application requires it. The polling of the keyboard effects the
drawing speed of the graphics board.









