ATI Technologies, Inc.,
3761 Victoria Park Avenue,
Scarborough, Ontario,  M1W 3S2
Tel:(416) 756-0718 Fax:(416) 756-0720
CompuServe: ATI Support 74740,667   GO ATITECH


Dual Monitor Operation with ATI Accelerator Video Boards


Introduction

ATI offers several products which will operate in a 
"dual monitor" setup; which one(s) you use will depend on your 
needs.

To achieve an "accelerator + text" setup, you'll need either an 
8514-ULTRA or a GRAPHICS ULTRA PRO for the accelerator side, and 
a VGA card for the other (an MDA, CGA, or EGA card could also be 
used for the text display).  The monitor attached to the VGA card
will display not only VGA text modes, but also any VGA or SVGA 
graphics.  The accelerator will only be active for applications 
which specifically access accelerated modes, through interfaces 
such as IBM 8514/a, or ATI "ULTRA".  Common applications which 
support these modes are Windows and several CAD packages.

Alternately, you may wish to achieve an "SVGA + text" setup.  
This is possible with a VGA or SVGA card plus an MDA card 
attached to a TTL monochrome monitor.  This setup provides a 
text-only display on one side, with a colour text, VGA and SVGA 
graphic display on the other.

There is, potentially, a third option.  With an advanced display 
adapter like the GRAPHICS ULTRA PRO, you could conceivably obtain 
all available graphics modes (both SVGA and accelerator) on one 
side, with a straight text MDA display on the other.  As shown 
below, the 8-bit MDA puts the PRO in 8-bit mode as well, so 
direct memory aperture functions are not available.


The GRAPHICS ULTRA PRO can coexist with another video adapter 
only if both are using the same "form of addressing".  An 8-bit 
video adapter (such as an MDA card) will require that the PRO 
operate in 8-bit mode as well.  Similarly, a 16-bit VGA adapter 
will require that the PRO be operating in 16-bit mode.

Operation in an 8-bit mode reduces the features of a video 
adapter to those which would be available in an 8-bit machine, 
such as the original IBM PC, or the later XT.  Of primary 
importance to us is that this mode reduces the amount of memory 
addressable by any component to 1MB.

In order for the mach32 chipset found on the PRO to take 
advantage of a "memory aperture" feature, in which the video 
memory is mapped directly into the system address space, it is
necessary that the card be capable of addressing memory above 
the 1MB limit.  Thus, the memory aperture feature is only 
available when the PRO is operating in 16-bit mode.

A normal VGA card uses a 64k block of memory, located at A000 
(just above the first 640k of RAM) to access the video memory.  
Since VGA and SVGA cards typically have up to 1MB of video memory
onboard, a "paging" scheme, similar to EMS, is required to map 
the desired portions of video memory into the "A-block" to be 
read or written by the CPU.  Since the A000 region is located 
within the first megabyte of RAM, this paging scheme is fully 
compatible with 8-bit operation.

The mach32 chipset incorporates an advanced feature called a 
"memory aperture", which can map the video RAM directly into 
the system address space.  This feature allows the CPU to directly
access the video memory, without the need to page it into a small 
64k window in the first megabyte.  The result is a reduction in 
processing time (ie better performance), since the overhead of the 
paging operation is removed.  To accomplish this, however, the 
mach32 requires access to memory regions above the first megabyte, 
and thus requires that it be operating in a 16-bit mode.

In addition to 16-bit operation, the memory aperture feature 
requires that there be sufficient empty memory space available on 
the bus.  On an ISA machine which has 16 megabytes of system RAM
installed, all available memory addresses on the bus are filled, 
hence the aperture cannot be enabled.  If the memory aperture 
cannot be enabled, whether due to a forced 8-bit operating mode,
or lack of available memory space on the bus, the mach32 must 
resort to the a method of paging that is quite similar to a 
standard VGA, using a 64k block at A000.  In the case of a mach32
product, like the GRAPHICS ULTRA PRO, this is known as a 
"virtual aperture" configuration.


Operating the EISA and ISA PRO in a Dual Monitor Setup with a VGA card:

Both cards must be in 16-bit operation, and the memory aperture 
feature of the mach32 must be enabled (in order to take advantage 
of memory aperture functions).  The VGA functions of the PRO
must be disabled via the DIP switches on the card. The EISA or ISA 
PRO must have a SVGA monitor connected and the VGA board must
have a VGA monitor connected. The passthrough cable must not
be used.

If the aperture must be disabled due to memory constraints, the 
mach32 is forced to use a paging scheme in the A000 region (to 
create a "virtual aperture").  Since the VGA card must also use 
this region to access it's video memory, the cards will conflict.  
This prevents the use of a mach32-specific driver.  "Engine-only" 
drivers, such as 8514/a or ATI mach8, which do not require access
to a virtual aperture in the A000 region should function normally 
in this configuration.


Operating the ISA PRO in a Dual Monitor Setup with an MDA card:

All MDA cards are 8-bit, so the PRO will also be operating in an 
8-bit mode.  The memory aperture must remain disabled in this 
configuration.  Memory access in the A000 region should not be a
problem, since the MDA card will use the B000 region instead.


24-bit Modes in Dual Adapter Configurations

There are three means available for creating 24-bit graphics 
displays on the GRAPHICS ULTRA PRO.  In order of decreasing 
performance they are: direct memory aperture, virtual aperture 
in the A000 block, and "engine-only" (no aperture access).

The direct memory aperture requires:

4MB free RAM address space on the bus
16-bit operation
Memory Aperture Enabled in INSTALL

Thus, a direct memory aperture is available on ISA systems with 
less than 12MB of system RAM and EISA and VLB systems with less 
than 124MB RAM, and in dual monitor configurations with a 16-bit
adapter (ie a VGA or SVGA card).

Currently, the mach32 Windows driver and the ULTRACAD AutoCAD 
display list driver can take advantage of a direct memory 
aperture for 24-bit modes.


A virtual memory aperture requires:

Free access to the A000 block
VGA circuitry on the PRO to be Enabled (DIP switches)
Memory Aperture Disabled in INSTALL

Thus, a virtual aperture is available on systems with any amount 
of RAM.  The only stipulation is that the PRO must be the only 
VGA card in the system.  Dual adapter configurations with an MDA 
should function normally.

Currently, the mach32 Windows driver and the ULTRACAD AutoCAD 
driver will take advantage of a virtual aperture for 24-bit modes.


An "engine-only" (no aperture) setup requires:

VGA circutiry on the PRO to be Disabled (DIP switches)
Memory Aperture Disabled in INSTALL

The "engine-only" configuration is compatible with any MDA, CGA, 
EGA or VGA secondary adapter, but is the slowest of the three 
configurations, especially in 24-bit colour mode.

Only the mach32 Windows driver is capable of utilitizing an 
"engine-only" configuration to produce 24-bit colour.