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Video Electronics Standards Association VBE/Core 2.0 Standard
2150 North First Street, Suite 440
San Jose, CA 95131-2029
Phone: (408) 435-0333
FAX: (408) 435-8225
VESA BIOS EXTENSION (VBE)
Core Functions
Version: 2.0
NOTE: This is _NOT_ an official version of the VBE/Core 2.0 standard,
but is provided as is by SciTech Software until the official
specification is made available electronically. This document
contains a summary of the important portions of the standard
related to developing working code for VBE 2.0.
For more information on the official specification, please
contact VESA at the address listed above.
1. Introduction
This document contains the VESA BIOS Extension (VBE) specification for
standard software access to graphics display controllers that support
resolutions, color depths, and frame buffer organizations beyond the
VGA hardware standard. It is intended for use by both applications
programmers and system software developers.
System software developers may use this document to supplement the
System and INT 10h ROM BIOS functions to provide the VBE services.
Application developers can use this document as a guide to programming
all VBE compatible devices.
To understand the VBE specification, some knowledge of 80x86 assembly
language and the VGA hardware registers may be required. However,
the services described in this specification may be called from any
high-level programming language that provides a mechanism for
generating software interrupts with the 80x86 registers set to user-
specified values.
In this specification, 'VBE' and 'VBE 2.0' are synonymous with 'VBE
Core Functions version 2.0'.
1.1. Scope of the VBE Standard
The primary purpose of the VESA VBE is to provide standard software
support for the many unique implementations of Super VGA (SVGA)
graphics controllers on the PC platform that provide features beyond
the original VGA hardware standard. This is to provide a feasible
mechanism by which application developers can take advantage of this
nonstandard hardware in graphics applications.
The VBE specification offers an extensible software foundation which
allows it to evolve as display and audio devices evolve over time,
without sacrificing backward software compatibility with older
implementations. New application software should be able to work with
older hardware, and application software that has already shipped
should work correctly on new hardware devices.
VBE services provide standard access to all resolutions and color
depths provided on the display controller, and report the availability
and details of all supported configurations to the application as
necessary.
VBE implementations facilitate the field support of audio and display
hardware by providing the application software with the manufacturer's
name and the product identification of the display hardware.
Since graphics controller services on the PC are typically implemented
in ROM, the VBE services are defined so that they should be
implemented within the standard VGA ROM. When ROM implementations of
VBE are not possible, or when field software upgrades to the onboard
ROM are necessary, the VBE implementation may be also offered as a
device driver or DOS Terminate & Stay Resident (TSR) program.
The standard VBE functions may be supplemented by OEM's as necessary
to support custom or proprietary functions unique to the manufacturer.
This mechanism enables the OEM to establish functions that may be
standard to the product line, or provide access to special hardware.
enhancements.
Although previous VBE standards assumed that the underlying graphics
architecture was a VGA device, the display services described by VBE
2.0 can be implemented on any frame buffer oriented graphics device.
The majority of VBE services facilitate the setup and configuration of
the hardware, allowing applications high performance, direct access to
the configured device at runtime. To further improve the performance
of flat frame buffer display devices in extended resolutions, VBE 2.0
provides new memory models that do not require the traditional frame
buffer "banking" mechanisms.
VBE is expected to work on all 80x86 platforms, in real and protected
modes.
Since some modern display devices are designed without any VGA
support, two display controllers may be present in the system. One
display controller would be used for VGA compatibility, and the other
used for graphic extensions to the basic VGA modes, resolutions, and
frame buffer models. Therefore, VBE must be able offer the
application automatic access to the appropriate device based on the
mode or resolution that is requested by the application.
Currently beyond the scope of the VBE specification is the handling of
hardware configuration and installation issues. It was originally
considered to become part of VBE 2.0, however we have deferred the
issues to the Graphics Configuration Supplemental Specification. In
addition, it is also possible for an OEM to define their own
extensions using the OEM Supplemental Specification if required.
1.2. Backgrounder
1
The IBM VGA has become a de facto standard in the PC graphics world.
A multitude of different VGA offerings exist in the marketplace, each
one providing BIOS or register compatibility with the IBM VGA. More
and more of these VGA compatible products implement various supersets
of the VGA standard. These extensions range from higher resolutions
and more colors to improved performance and even some graphics
processing capabilities. Intense competition has dramatically improved
the price/performance ratio, to the benefit of the end user.
However, several serious problems face a software developer who
intends to take advantage of these "Super VGA" environments. Because
there is no standard hardware implementation, the developer is faced
with widely disparate Super VGA hardware architecture. Lacking a
common software interface, designing applications for these
environments is costly and technically difficult. Except for
applications supported by OEM-specific display drivers, very few
software packages can take advantage of the power and capabilities of
Super VGA products.
The VBE standard was originally conceived to enable the development of
applications that wished to take advantage of display resolutions and
color depths beyond the VGA definition. The need for an application
or software standard was recognized by the developers of graphic
hardware to encourage the use and acceptance of their rapidly
advancing product families. It became obvious that the majority of
software application developers did not have the resources to develop
and support custom device level software for the hundreds of display
boards on the market. Therefore the rich new features of these
display devices were not being used outside of the relatively small
CAD market, and only then after considerable effort.
Indeed, the need for a standard for SVGA display adapters became so
important that the VESA organization was formed to seek out a
solution. The original VBE standard was devised and agreed upon by
each of the active display controller manufacturers, and has since
been adopted by DOS application developers to enable use of non-VGA
extended display modes.
As time went along VBE 1.1 was created to add more video modes and
increased logical line length/double buffering support. VBE 1.2 was
created to add modes and also added high color RAMDAC support.
In the three years since VBE 1.2 was approved we have seen the
standard become widely accepted and many successful programs have
embraced VBE. However, it has become obvious that the need for a more
robust and extensible standard exists. Early extensions to the VGA
standard continued using all of the original VGA I/O ports and frame
buffer address to communicate with the controller hardware. As we've
seen, the supported resolutions and color depths have grown,
intelligent controllers with BITBLT and LineDraw Functions have become
common, and new flat frame buffer memory models have appeared along
with display controllers that are not based on VGA in any way. VBE
2.0 and future extensions will support non-VGA based controllers with
new functions for reading and writing the palette and for access to
the flat frame buffer models.
VBE 2.0, as designed, offers the extensibility and the robustness that
was lacking in the previous specifications, while at the same time
offering backwards compatibility.
In the future, we see the need for adding supplemental specifications
for issues like Multimedia; Advanced Graphics Functions; and "Plug and
Play" features.
2.VBE Overview
This chapter outlines the various features and limitations of the VBE
standard.
2.1. VBE Features
Standard application interface to Graphics Controllers (SVGA
Devices)
Standard method of identifying products and manufacturers.
Provision for OEM extensions through Sub-function 14h
Simple protected mode interface.
Extensible interface through supplemental specifications.
2.2. VBE Affected Devices
All frame buffer-based devices in the IBM PC platform (with the
exception of Hercules, Monochrome (MDA), CGA and EGA devices) are
suitable for use within the VBE standard to enable access to the
device by VBE-compliant applications.
2.3. Providing Vendor Information
The VGA specification does not provide a standard mechanism to
determine what graphic hardware it is running on. Only by knowing OEM-
specific features can an application determine the presence of a
particular graphics controller or display board. This often involves
reading and testing registers located at I/O addresses unique to each
OEM. By not knowing what hardware an application is running on, few,
if any, of the extended features of the underlying hardware can be
used.
The VESA BIOS Extension provides several functions to return
information about the graphics environment. These functions return
system level information as well as graphics mode specific details.
Function 00h returns general system level information, including an
OEM identification string. The function also returns a pointer to the
supported VBE and OEM modes. Function 01h may be used by the
application to obtain additional information about each supported
mode. Function 03h returns the current VBE mode.
3.VBE Mode Numbers
Standard VGA mode numbers are 7 bits wide and presently range from 00h
to 13h. OEMs have defined extended display modes in the range 14h to
7Fh. Values in the range 80h to FFh cannot be used, since VGA BIOS
Function 00h (Set video mode) interprets bit 7 as a flag to clear or
preserve display memory.
Due to the limitations of 7 bit mode numbers, the optional VBE mode
numbers are 14 bits wide. To initialize a VBE mode, the mode number is
passed in the BX register to VBE Function 02h (Set VBE mode).
The format of VBE mode numbers is as follows:
D0-D8 = Mode number
If D8 == 0, this is not a VESA defined mode
If D8 == 1, this is a VESA defined mode
D9-D13 = Reserved by VESA for future expansion (= 0)
D14 = Linear/Flat Frame Buffer Select
If D14 == 0, Use VGA Frame Buffer
If D14 == 1, Use Linear/Flat Frame Buffer
D15 = Preserve Display Memory Select
If D15 == 0, Clear display memory
If D14 == 1, Preserve display memory
Thus, VBE mode numbers begin at 100h. This mode numbering scheme
implements standard 7-bit mode numbers for OEM-defined modes.
Standard VGA modes may be initialized through VBE Function 02h (Set
VBE mode) simply by placing the mode number in BL and clearing the
upper byte (BH). 7-bit OEM-defined display modes may be initialized in
the same way. Note that modes may only be set if the mode exists in
the Video Mode List returned in Function 0.
Note: Starting with VBE version 2.0 VESA will no longer define new
VESA mode numbers and it will not longer be mandatory to support these
old mode numbers. However, it is highly recommended that BIOS
implementations continue to support these mode numbers for
compatibility with old software. VBE 2.0-aware applications should
follow the guidelines in Appendix 5 - Application Programming
Considerations - for setting a desired mode.
Note: Mode 81FFh is a special mode designed to preserve the current
memory contents and to give access to the entire video memory. This
mode is especially useful for saving the entire video memory contents
before going into a state that could lose the contents (e.g. set this
mode to gain access to all video memory to save it before going into a
volatile power down state). This mode is required because the entire
video memory contents are not always accessible in every mode. It is
recommended that this mode be packed pixel in format, and a
ModeInfoBlock must be defined for it. Look in the ModeInfoBlock to
determine if paging is required and how paging is supported if it is.
Also note that there are no implied resolutions or timings associated
with this mode.
Note: Future display resolutions will be defined by VESA display
vendors. The color depths will not be specified and new mode numbers
will not be assigned for these resolutions. For example, if the VESA
display vendors define 1600x1200 as a VESA resolution, application
developers should target their display resolution for 1600x1200 rather
than choosing an arbitrary resolution like 1550x1190. The VBE
implementation should be queried to get the available resolutions and
color depths and the application should be flexible enough to work
with this list. Appendix 5 gives a detailed summary of the way an
application should go about selecting and setting modes.
4.VBE Functions
This chapter describes in detail each of the functions defined by the
VBE standard. VBE functions are called using the INT 10h interrupt
vector, passing arguments in the 80X86 registers. The INT 10h
interrupt handler first determines if a VBE function has been
requested, and if so, processes that request. Otherwise control is
passed to the standard VGA BIOS for completion.
All VBE functions are called with the AH register set to 4Fh to
distinguish them from the standard VGA BIOS functions. The AL
register is used to indicate which VBE function is to be performed.
For supplemental or extended functionality the BL register is used
when appropriate to indicate a specific sub-function.
Functions 00-0Fh have been reserved for Standard VBE function numbers;
Functions 10-FFh are reserved for VBE Supplemental Specifications.
In addition to the INT 10h interface, a Protected Mode Interface is
available and is described below.
4.1. VBE Return Status
The AX register is used to indicate the completion status upon return
from VBE functions. If VBE support for the specified function is
available, the 4Fh value passed in the AH register on entry is
returned in the AL register. If the VBE function completed
successfully, 00h is returned in the AH register. Otherwise the AH
register is set to indicate the nature of the failure.
VBE RETURN STATUS
AL == 4Fh: Function is supported
AL != 4Fh: Function is not supported
AH == 00h: Function call successful
AH == 01h: Function call failed
AH == 02h: Software supports this function, but the hardware
does not
AH == 03h: Function call invalid in current video mode
Note: Applications should treat any non-zero value in the AH register
as a general failure condition as later versions of the VBE may define
additional error codes.
4.2. Protected Mode considerations
VBE services may be called directly from 32-bit Protected mode only.
For 32 bit protected mode, 2 selector/segment descriptors for 32-bit
code and the data segment are needed. These will be allocated and
initialized by the caller. The segment limit fields will be set to
64k. These selectors may either be in the GDT or LDT, but must be
valid whenever the VBE is called in protected mode. The caller must
supply a stack large enough for use by VBE and by potential interrupt
handlers. The caller's stack will be active if or when interrupts are
enabled in the VBE routine, since the VBE will not switch stacks when
interrupts are enabled, including NMI interrupts. The 32-bit VBE
interface requires a 32-bit stack.
When the VBE services are called, the current I/O permission bit map
must allow access to the I/O ports that the VBE may need to access.
This can be found in the Sub-table (Ports and Memory) returned by VBE
Function 0Ah.
To summarize, it is the calling application's responsibility to ensure
to that it has the appropriate I/O and memory privileges, a large
enough stack and appropriate selectors allocated. It is also the
calling application's responsibility to preserve registers if it needs
them.
4.3. Function 00h - Return VBE Controller Information
This required function returns the capabilities of the display
controller, the revision level of the VBE implementation, and vendor
specific information to assist in supporting all display controllers
in the field.
The purpose of this function is to provide information to the calling
program about the general capabilities of the installed VBE software
and hardware. This function fills an information block structure at
the address specified by the caller. The VbeInfoBlock information
block size is 256 bytes for VBE 1.x, and 512 bytes for VBE 2.0.
Input: AX = 4F00h Return VBE Controller Information
ES:DI = Pointer to buffer in which to place
VbeInfoBlock structure
(VbeSignature should be set to 'VBE2' when
function is called to indicate VBE 2.0
information is desired and the information
block is 512 bytes in size.)
Output: AX = VBE Return Status
Note: All other registers are preserved.
The information block has the following structure:
VbeInfoBlock struc
VbeSignature db 'VESA' ; VBE Signature
VbeVersion dw 0200h ; VBE Version
OemStringPtr dd ? ; Pointer to OEM String
Capabilities db 4 dup (?) ; Capabilities of graphics cont.
VideoModePtr dd ? ; Pointer to Video Mode List
TotalMemory dw ? ; Number of 64kb memory blocks
; Added for VBE 2.0
OemSoftwareRev dw ? ; VBE implementation Software revision
OemVendorNamePtr dd ? ; Pointer to Vendor Name String
OemProductNamePtr dd ? ; Pointer to Product Name String
OemProductRevPtr dd ? ; Pointer to Product Revision String
Reserved db 222 dup (?); Reserved for VBE implementation
; scratch area
OemData db 256 dup (?); Data Area for OEM Strings
VbeInfoBlock ends
Note: All data in this structure is subject to change by the VBE
implementation when VBE Function 00h is called. Therefore, it should
not be used by the application to store data of any kind.
Description of the VbeInfoBlock structure fields:
The VbeSignature field is filled with the ASCII characters 'VESA' by
the VBE implementation. VBE 2.0 applications should preset this field
with the ASCII characters 'VBE2' to indicate to the VBE implementation
that the VBE 2.0 extended information is desired, and the VbeInfoBlock
is 512 bytes in size. Upon return from VBE Function 00h, this field
should always be set to 'VESA' by the VBE implementation.
The VbeVersion is a BCD value which specifies what level of the VBE
standard is implemented in the software. The higher byte specifies the
major version number. The lower byte specifies the minor version
number.
Note: The BCD value for VBE 2.0 is 0200h and the BCD value for VBE
1.2 is 0102h. In the past we have had some applications
misinterpreting these BCD values. For example, BCD 0102h was
interpreted as 1.02, which is incorrect.
The OemStringPtr is a Real Mode far pointer to a null terminated OEM-
defined string. This string may be used to identify the graphics
controller chip or OEM product family for hardware specific display
drivers. There are no restrictions on the format of the string. This
pointer may point into either ROM or RAM, depending on the specific
implementation. VBE 2.0 BIOS implementations must place this string
in the OemData area within the VbeInfoBlock if 'VBE2' is preset in the
VbeSignature field on entry to Function 00h. This makes it possible
to convert the RealMode address to an offset within the VbeInfoBlock
for Protected mode applications.
Note: The length of the OEMString is not defined, but for space
considerations, we recommend a string length of less than 256 bytes.
The Capabilities field indicates the support of specific features in
the graphics environment. The bits are defined as follows:
D0 = 0 DAC is fixed width, with 6 bits per primary color
= 1 DAC width is switchable to 8 bits per primary color
D1 = 0 Controller is VGA compatible
= 1 Controller is not VGA compatible
D2 = 0 Normal RAMDAC operation
= 1 When programming large blocks of information to the
RAMDAC use blank bit in Function 09h. i.e. RAMDAC
recommends programming during blank period only.
D3-31 = Reserved
BIOS Implementation Note: The DAC must always be restored to 6 bits
per primary as default upon a mode set. If the DAC has been switched
to 8 bits per primary, the mode set must restore the DAC to 6 bits per
primary to ensure the application developer that he does not have to
reset it.
Application Developer's Note: If a DAC is switchable, you can assume
that the DAC will be restored to 6 bits per primary upon a mode set.
For an application to use a DAC the application program is responsible
for setting the DAC to 8 bits per primary mode using Function 08h.
VGA compatibility is defined as supporting all standard IBM VGA modes,
fonts and I/O ports; however, VGA compatibility doesn't guarantee that
all modes which can be set are VGA compatible, or that the 8x14 font
is available.
The need for D2 = 1 "program the RAMDAC using the blank bit in
Function 09h" is for older style RAMDAC's where programming the RAM
values during display time causes a "snow-like" effect on the screen.
Newer style RAMDAC's don't have this limitation and can easily be
programmed at any time, but older RAMDAC's require the that they be
blanked so as not to display the snow while values change during
display time.. This bit informs the software that they should make
the function call with 80h rather than 00h to ensure the minimization
of the "snow-like" effect.
The VideoModePtr points to a list of mode numbers for all display
modes supported by the VBE implementation. Each mode number occupies
one word (16 bits). The list of mode numbers is terminated by a -1
(0FF Vh). The mode numbers in this list represent all of the
potentially supported modes by the display controller. Please refer
to Chapter 3 for a description of VESA VBE mode numbers. VBE 2.0 BIOS
implementations must place this mode list in the Reserved area in the
VbeInfoBlock or have it statically stored within the VBE
implementation if 'VBE2' is preset in the VbeSignature field on entry
to Function 00h.
Note: It is the application's responsibility to verify the actual
availability of any mode returned by this function through the Return
VBE Mode Information (VBE Function 01h) call. Some of the returned
modes may not be available due to the actual amount of memory
physically installed on the display board or due to the capabilities
of the attached monitor.
Note: If a VideoModeList is found to contain no entries (starts with
0F VBh), it can be assumed that the VBE implementation is a "stub"
implementation where only Function 00h is supported for diagnostic or
"Plug and Play" reasons. These stub implementations are not VBE 2.0
compliant and should only be implemented in cases where no space is
available to implement the whole VBE.
The TotalMemory field indicates the maximum amount of memory
physically installed and available to the frame buffer in 64KB units.
(e.g. 256KB = 4, 512KB = 8) Not all video modes can address all this
memory, see the ModeInfoBlock for detailed information about the
addressible memory for a given mode.
The OemSoftwareRev field is a BCD value which specifies the OEM
revision level of the VBE software. The higher byte specifies the
major version number. The lower byte specifies the minor version
number. This field can be used to identify the OEM's VBE software
release. This field is only filled in when 'VBE2' is preset in the
VbeSignature field on entry to Function 00h.
The OemVendorNamePtr is a pointer to a null-terminated string
containing the name of the vendor who produced the display controller
board product. (This string may be contained in the VbeInfoBlock or
the VBE implementation.) This field is only filled in when 'VBE2' is
preset in the VbeSignature field on entry to Function 00h. (Note:
the length of the strings OemProductRev, OemProductName and
OemVendorName (including terminators) summed, must fit within a 256
byte buffer; this is to allow for return in the OemData field if
necessary.)
The OemProductNamePtr is a pointer to a null-terminated string
containing the product name of the display controller board. (This
string may be contained in the VbeInfoBlock or the VBE
implementation.) This field is only filled in when 'VBE2' is preset
in the VbeSignature field on entry to Function 00h. (Note: the
length of the strings OemProductRev, OemProductName and OemVendorName
(including terminators) summed, must fit within a 256 byte buffer;
this is to allow for return in the OemData field if necessary.)
The OemProductRevPtr is a pointer to a null-terminated string
containing the revision or manufacturing level of the display
controller board product. (This string may be contained in the
VbeInfoBlock or the VBE implementation.) This field can be used to
determine which production revision of the display controller board is
installed. This field is only filled in when 'VBE2' is preset in the
VbeSignature field on entry to Function 00h. (Note: the length of
the strings OemProductRev, OemProductName and OemVendorName (including
terminators) summed, must fit within a 256 byte buffer; this is to
allow for return in the OemData field if necessary.)
The Reserved field is a space reserved for dynamically building the
VideoModeList if necessary if the VideoModeList is not statically
stored within the VBE implementation. This field should not be used
for anything else, and may be reassigned in the future. Application
software should not assume that information in this field is valid.
The OemData field is a 256 byte data area that is used to return OEM
information returned by VBE Function 00h when 'VBE2' is preset in the
VbeSignature field. The OemVendorName string, OemProductName string
and OemProductRev string are copied into this area by the VBE
implementation. This area will only be used by VBE implementations
2.0 and above when 'VBE2' is preset in the VbeSignature field.
4.4. Function 01h - Return VBE Mode Information
This required function returns extended information about a specific
VBE display mode from the mode list returned by VBE Function 00h.
This function fills the mode information block, ModeInfoBlock,
structure with technical details on the requested mode. The
ModeInfoBlock structure is provided by the application with a fixed
size of 256 bytes.
Information can be obtained for all listed modes in the Video Mode
List returned in Function 00h. If the requested mode cannot be used
or is unavailable, a bit will be set in the ModeAttributes field to
indicate that the mode is not supported in the current configuration.
Input: AX = 4F01h Return VBE mode information
CX = Mode number
ES:DI = Pointer to ModeInfoBlock structure
Output: AX = VBE Return Status
Note: All other registers are preserved.
The mode information block has the following structure:
ModeInfoBlock struc
; Mandatory information for all VBE revisions
ModeAttributes dw ? ; mode attributes
WinAAttributes db ? ; window A attributes
WinBAttributes db ? ; window B attributes
WinGranularity dw ? ; window granularity
WinSize dw ? ; window size
WinASegment dw ? ; window A start segment
WinBSegment dw ? ; window B start segment
WinFuncPtr dd ? ; pointer to window function
BytesPerScanLine dw ? ; bytes per scan line
; Mandatory information for VBE 1.2 and above
XResolution dw ? ; horizontal resolution in pixels or chars
YResolution dw ? ; vertical resolution in pixels or chars
XCharSize db ? ; character cell width in pixels
YCharSize db ? ; character cell height in pixels
NumberOfPlanes db ? ; number of memory planes
BitsPerPixel db ? ; bits per pixel
NumberOfBanks db ? ; number of banks
MemoryModel db ? ; memory model type
BankSize db ? ; bank size in KB
NumberOfImagePages db ? ; number of images
Reserved db ? ; reserved for page function
; Direct Color fields (required for direct/6 and YUV/7 memory models)
RedMaskSize db ? ; size of direct color red mask in bits
RedFieldPosition db ? ; bit position of lsb of red mask
GreenMaskSize db ? ; size of direct color green mask in bits
GreenFieldPosition db ? ; bit position of lsb of green mask
BlueMaskSize db ? ; size of direct color blue mask in bits
BlueFieldPosition db ? ; bit position of lsb of blue mask
RsvdMaskSize db ? ; size of direct color reserved mask in bits
RsvdFieldPosition db ? ; bit position of lsb of reserved mask
DirectColorModeInfo db ? ; direct color mode attributes
; Mandatory information for VBE 2.0 and above
PhysBasePtr dd ? ; physical address for flat frame buffer
OffScreenMemOffset dd ? ; pointer to start of off screen memory
OffScreenMemSize dw ? ; amount of off screen memory in 1k units
Reserved db 206 dup (?) ; remainder of ModeInfoBlock
ModeInfoBlock ends
The ModeAttributes field describes certain important characteristics
of the graphics mode.
The ModeAttributes field is defined as follows:
D0 = Mode supported by hardware configuration
0 = Mode not supported in hardware
1 = Mode supported in hardware
D1 = 1 (Reserved)
D2 = TTY Output functions supported by BIOS
0 = TTY Output functions not supported by BIOS
1 = TTY Output functions supported by BIOS
D3 = Monochrome/color mode (see note below)
0 = Monochrome mode
1 = Color mode
D4 = Mode type
0 = Text mode
1 = Graphics mode
D5 = VGA compatible mode
0 = Yes
1 = No
D6 = VGA compatible windowed memory mode is available
0 = Yes
1 = No
D7 = Linear frame buffer mode is available
0 = No
1 = Yes
D8-D15 = Reserved
Bit D0 is set to indicate that this mode can be initialized in the
present hardware configuration. This bit is reset to indicate the
unavailability of a graphics mode if it requires a certain monitor
type, more memory than is physically installed, etc.
Bit D1 was used by VBE 1.0 and 1.1 to indicate that the optional
information following the BytesPerScanLine field were present in the
data structure. This information became mandatory with VBE version
1.2 and above, so D1 is no longer used and should be set to 1. The
Direct Color fields are valid only if the MemoryModel field is set to
a 6 (Direct Color) or 7 (YUV).
Bit D2 indicates whether the video BIOS has support for output
functions like TTY output, scroll, etc. in this mode. TTY support is
recommended but not required for all extended text and graphic modes.
If bit D2 is set to 1, then the INT 10h BIOS must support all of the
standard output functions listed below.
All of the following TTY functions must be supported when this bit is
set:
01 Set Cursor Size
02 Set Cursor Position
06 Scroll TTY window up or Blank Window
07 Scroll TTY window down or Blank Window
09 Write character and attribute at cursor position
0A Write character only at cursor position
0E Write character and advance cursor
Bit D3 is set to indicate color modes, and cleared for monochrome
modes.
Bit D4 is set to indicate graphics modes, and cleared for text modes.
Note: Monochrome modes map their CRTC address at 3B4h. Color modes map
their CRTC address at 3D4h. Monochrome modes have attributes in which
only bit 3 (video) and bit 4 (intensity) of the attribute controller
output are significant. Therefore, monochrome text modes have
attributes of off, video, high intensity, blink, etc. Monochrome
graphics modes are two plane graphics modes and have attributes of
off, video, high intensity, and blink. Extended two color modes that
have their CRTC address at 3D4h, are color modes with one bit per
pixel and one plane. The standard VGA modes, 06h and 11h would be
classified as color modes, while the standard VGA modes 07h and 0Fh
would be classified as monochrome modes.
Bit D5 is used to indicate if the mode is compatible with the VGA
hardware registers and I/O ports. If this bit is set, then the mode
is NOT VGA compatible and no assumptions should be made about the
availability of any VGA registers. If clear, then the standard VGA
I/O ports and frame buffer address defined in WinASegment and/or
WinBSegment can be assumed.
Bit D6 is used to indicate if the mode provides Windowing or Banking
of the frame buffer into the frame buffer memory region specified by
WinASegment and WinBSegment. If set, then Windowing of the frame
buffer is NOT possible. If clear, then the device is capable of
mapping the frame buffer into the segment specified in WinASegment
and/or WinBSegment. (This bit is used in conjunction with bit D7, see
table following D7 for usage)
Bit D7 indicates the presence of a Linear Frame Buffer memory model.
If this bit is set, the display controller can be put into a flat
memory model by setting the mode (VBE Function 02h) with the Flat
Memory Model bit set. (This bit is used in conjunction with bit D6,
see following table for usage)
+-- 0 =+- +- +
| | D7 | D6 |
+- 0 = +- +- +
| Windowed | 0 | 0 |
| frame | | |
| buffer | | |
| only | | |
+- 0 = +- +- +
| n/a | 0 | 1 |
+- 0 = +- +- +
| Both | 1 | 0 |
| Windowed | | |
| and 4 | | |
| Linear | | |
+- 0 = +- +- +
| Linear | 1 | 1 |
| frame | | |
| buffer | | |
| only | | |
+- 0 = +- +- +
The BytesPerScanLine field specifies how many full bytes are in each
logical scanline. The logical scanline could be equal to or larger
than the displayed scanline.
The WinAAttributes and WinBAttributes describe the characteristics of
the CPU windowing scheme such as whether the windows exist and are
read/writeable, as follows:
D0 = Relocatable window(s) supported
0 = Single non-relocatable window only
1 = Relocatable window(s) are supported
D1 = Window readable
0 = Window is not readable
1 = Window is readable
D2 = Window writeable
0 = Window is not writeable
1 = Window is writeable
D3-D7 = Reserved
Even if windowing is not supported, (bit D0 = 0 for both Window A and
Window B), then an application can assume that the display memory
buffer resides at the location specified by WinASegment and/or
WinBSegment.
WinGranularity specifies the smallest boundary, in KB, on which the
window can be placed in the frame buffer memory. The value of this
field is undefined if Bit D0 of the appropriate WinAttributes field is
not set.
WinSize specifies the size of the window in KB.
WinASegment and WinBSegment address specify the segment addresses
where the windows are located in the CPU address space.
Use D14 of the Mode Number to select the Linear Buffer on a mode set
(Function 02h).
WinFuncPtr specifies the segment:offset of the VBE memory windowing
function. The windowing function can be invoked either through VBE
Function 05h, or by calling the function directly. A direct call will
provide faster access to the hardware paging registers than using VBE
Function 05h, and is intended to be used by high performance
applications. If this field is NULL, then VBE Function 05h must be
used to set the memory window when paging is supported. This direct
call method uses the same parameters as VBE Function 05h including AX
and for VBE 2.0 implementations will return the correct Return Status.
VBE 1.2 implementations and earlier, did not require the Return Status
information to be returned. For more information on the direct call
method, see the notes in VBE Function 05h and the sample code in
Appendix 5.
The XResolution and YResolution specify the width and height in pixel
elements or characters for this display mode. In graphics modes, these
fields indicate the number of horizontal and vertical pixels that may
be displayed. In text modes, these fields indicate the number of
horizontal and vertical character positions. The number of pixel
positions for text modes may be calculated by multiplying the returned
XResolution and YResolution values by the character cell width and
height indicated in the XCharSize and YCharSize fields described
below.
The XCharSize and YCharSize specify the size of the character cell in
pixels. (This value is not zero based) e.g. XCharSize for Mode 3
using the 9 point font will have a value of 9.
The NumberOfPlanes field specifies the number of memory planes
available to software in that mode. For standard 16-color VGA
graphics, this would be set to 4. For standard packed pixel modes, the
field would be set to 1. For 256-color non-chain-4 modes, where you
need to do banking to address all pixels this value should be set to
the number of banks required to get to all the pixels (typically this
will be 4 or 8).
The BitsPerPixel field specifies the total number of bits allocated to
one pixel. For example, a standard VGA 4 Plane 16-color graphics mode
would have a 4 in this field and a packed pixel 256-color graphics
mode would specify 8 in this field. The number of bits per pixel per
plane can normally be derived by dividing the BitsPerPixel field by
the NumberOfPlanes field.
The MemoryModel field specifies the general type of memory
organization used in this mode. The following models have been
defined:
00h = Text mode
01h = CGA graphics
02h = Hercules graphics
03h = Planar
04h = Packed pixel
05h = Non-chain 4, 256 color
06h = Direct Color
07h = YUV
08h-0Fh = Reserved, to be defined by VESA
10h-FFh = To be defined by OEM
VBE Version 1.1 and earlier defined Direct Color graphics modes with
pixel formats 1:5:5:5, 8:8:8, and 8:8:8:8 as a Packed Pixel model
with 16, 24, and 32 bits per pixel, respectively. In VBE Version 1.2.
and later, the Direct Color modes use the Direct Color memory model
and use the MaskSize and FieldPosition fields of the ModeInfoBlock to
describe the pixel format. BitsPerPixel is always defined to be the
total memory size of the pixel, in bits.
NumberOfBanks. This is the number of banks in which the scan lines are
grouped. The quotient from dividing the scan line number by the number
of banks is the bank that contains the scan line and the remainder is
the scan line number within the bank. For example, CGA graphics modes
have two banks and Hercules graphics mode has four banks. For modes
that don't have scanline banks (such as VGA modes 0Dh-13h), this field
should be set to 1.
The BankSize field specifies the size of a bank (group of scan lines)
in units of 1 KB. For CGA and Hercules graphics modes this is 8, as
each bank is 8192 bytes in length. For modes that don't have scanline
banks (such as VGA modes 0Dh-13h), this field should be set to 0.
The NumberOfImagePages field specifies the "total number minus one (-
1)"of complete display images that will fit into the frame buffer
memory. The application may load more than one image into the frame
buffer memory if this field is non-zero, and move the display window
within each of those pages. This should only be used for determining
the additional display pages which are available to the application;
to determine the available off screen memory, use the
OffScreenMemOffset and OffScreenMemSize information.
Note: If the ModeInfoBlock is for an IBM Standard VGA mode and the
NumberOfImagePages field contains more pages than would be found in a
256KB implementation, the TTY support described in the ModeAttributes
must be accurate. i.e. if the TTY functions are claimed to be
supported, they must be supported in all pages, not just the pages
normally found in the 256KB implementation.
The Reserved field has been defined to support a future VBE feature
and will always be set to one in this version.
The RedMaskSize, GreenMaskSize, BlueMaskSize, and RsvdMaskSize fields
define the size, in bits, of the red, green, and blue components of a
direct color pixel. A bit mask can be constructed from the MaskSize
fields using simple shift arithmetic. For example, the MaskSize values
for a Direct Color 5:6:5 mode would be 5, 6, 5, and 0, for the red,
green, blue, and reserved fields, respectively. Note that in the YUV
MemoryModel, the red field is used for V, the green field is used for
Y, and the blue field is used for U. The MaskSize fields should be set
to 0 in modes using a memory model that does not have pixels with
component fields.
The RedFieldPosition, GreenFieldPosition, BlueFieldPosition, and
RsvdFieldPosition fields define the bit position within the direct
color pixel or YUV pixel of the least significant bit of the
respective color component. A color value can be aligned with its
pixel field by shifting the value left by the FieldPosition. For
example, the FieldPosition values for a Direct Color 5:6:5 mode would
be 11, 5, 0, and 0, for the red, green, blue, and reserved fields,
respectively. Note that in the YUV MemoryModel, the red field is used
for V, the green field is used for Y, and the blue field is used for
U. The FieldPosition fields should be set to 0 in modes using a memory
model that does not have pixels with component fields.
The DirectColorModeInfo field describes important characteristics of.
direct color modes. Bit D0 specifies whether the color ramp of the
DAC is fixed or programmable. If the color ramp is fixed, then it can
not be changed. If the color ramp is programmable, it is assumed that
the red, green, and blue lookup tables can be loaded by using VBE
Function 09h. Bit D1 specifies whether the bits in the Rsvd field of
the direct color pixel can be used by the application or are reserved,
and thus unusable.
D0 = Color ramp is fixed/programmable
0 = Color ramp is fixed
1 = Color ramp is programmable
D1 = Bits in Rsvd field are usable/reserved
0 = Bits in Rsvd field are reserved
1 = Bits in Rsvd field are usable by the application
The PhysBasePtr is a 32 bit physical address of the start of frame
buffer memory when the controller is in flat frame buffer memory mode.
If this mode is not available, then this field will be zero.
The OffScreenMemOffset is a 32 bit offset from the start of the frame
buffer memory. Extra off-screen memory that is needed by the
controller may be located either before or after this off screen
memory, be sure to check OffScreenMemSize to determine the amount of
off-screen memory which is available to the application.
The OffScreenMemSize contains the amount of available, contiguous off-
screen memory in 1k units, which can be used by the application.
Note: Version 1.1 and later VBE will zero out all unused fields in the
Mode Information Block, always returning exactly 256 bytes. This
facilitates upward compatibility with future versions of the standard,
as any newly added fields will be designed such that values of zero
will indicate nominal defaults or non-implementation of optional
features. (For example, a field containing a bit-mask of extended
capabilities would reflect the absence of all such capabilities.)
Applications that wish to be backwards compatible to Version 1.0 VBE
should pre-initialize the 256 byte buffer before calling the Return
VBE Mode Information function.
4.5. Function 02h - Set VBE Mode
This required function initializes the controller and sets a VBE mode.
The format of VESA VBE mode numbers is described earlier in this
document. If the mode cannot be set, the BIOS should leave the
graphics environment unchanged and return a failure error code.
Input: AX = 4F02h Set VBE Mode
BX = Desired Mode to set
D0-D8 = Mode number
D9-D13 = Reserved (must be 0)
D14 = 0 Use windowed frame buffer model
= 1 Use linear/flat frame buffer model
D15 = 0 Clear display memory
= 1 Don't clear display memory
Output: AX = VBE Return Status
Note: All other registers are preserved.
If the requested mode number is not available, then the call will
fail, returning AH=01h to indicate the failure to the application.
If bit D14 is set, the mode will be initialized for use with a flat
frame buffer model. The base address of the frame buffer can be
determined from the extended mode information returned by VBE Function
01h. If D14 is set, and a linear frame buffer model is not available
then the call will fail, returning AH=01h to the application.
If bit D15 is not set, all reported image pages, based on Function 00h
returned information NumberOfImagePages, will be cleared to 00h in
graphics mode, and 20 07 in text mode. Memory over and above the
reported image pages will not be changed. If bit D15 is set, then the
contents of the frame buffer after the mode change is undefined.
Note, the 1-byte mode numbers used in Function 00h of an IBM VGA
compatible BIOS use D7 to signify the same thing as D15 does in this
function. If D7 is set for an IBM compatible mode set using this
Function (02), this mode set will fail. VBE aware applications must
use the memory clear bit in D15.
Note: VBE BIOS 2.0 implementations should also update the BIOS Data
Area 40:87 memory clear bit so that VBE Function 03h can return this
flag. VBE BIOS 1.2 and earlier implementations ignore the memory clear
bit.
Note: This call should not set modes not listed in the list of
supported modes. In addition all modes (including IBM standard VGA
modes), if listed as supported, must have ModeInfoBlock structures
associated with them. Required ModeInfoBlock values for the IBM
Standard Modes are listed in Appendix 2.
Note: If there is a failure when selecting an unsupported D14 value,
the error return should be 02h.
4.6. Function 03h - Return current VBE Mode
This required function returns the current VBE mode. The format of VBE
mode numbers is described earlier in this document.
Input: AX = 4F03h Return current VBE Mode
Output: AX = VBE Return Status
BX = Current VBE mode
D0-D13 = Mode number
D14 = 0 Windowed frame buffer model
= 1 Linear/flat frame buffer model
D15 = 0 Memory cleared at last mode set
= 1 Memory not cleared at last mode set
Note: All other registers are preserved.
Version 1.x Note: In a standard VGA BIOS, Function 0Fh (Read current
video state) returns the current graphics mode in the AL register. In
D7 of AL, it also returns the status of the memory clear bit (D7 of
40:87). This bit is set if the mode was set without clearing memory.
In this VBE function, the memory clear bit will not be returned in BX
since the purpose of the function is to return the video mode only. If
an application wants to obtain the memory clear bit, it should call
the standard VGA BIOS Function 0Fh.
Version 2.x Note: Unlike version 1.x VBE implementations, the memory
clear flag will be returned. The application should NOT call the
standard VGA BIOS Function 0Fh if the mode was set with VBE Function
02h.
Note: The mode number returned must be the same mode number used in
the VBE Function 02h mode set.
Note: This function is not guaranteed to return an accurate mode value
if the mode set was not done with VBE Function 02h.
4.7. Function 04h - Save/Restore state
This required function provides a complete mechanism to save and
restore the display controller hardware state. The functions are a
superset of the three subfunctions under the standard VGA BIOS
Function 1Ch (Save/restore state) which does not guarantee that the
extended registers of the video device are saved or restored. The
complete hardware state (except frame buffer memory) should be
saveable/restorable by setting the requested states mask (in the CX
register) to 000Fh.
Input: AX = 4F04h Save/Restore state
DL = 00h Return save/restore state buffer size
= 01h Save state
= 02h Restore state
CX = Requested states
D0= Save/restore controller hardware state
D1= Save/restore BIOS data state
D2= Save/restore DAC state
D3= Save/restore Register state
ES:BX= Pointer to buffer (if DL <> 00h)
Output: AX = VBE Return Status
BX = Number of 64-byte blocks to hold the state
buffer (if DL=00h)
Note: All other registers are preserved.
4.8. Function 05h - Display Window Control
This required function sets or gets the position of the specified
display window or page in the frame buffer memory by adjusting the
necessary hardware paging registers. To use this function properly,
the software should first use VBE Function 01h (Return VBE Mode
information) to determine the size, location and granularity of the
windows.
For performance reasons, it may be more efficient to call this
function directly, without incurring the INT 10h overhead. VBE
Function 01h returns the segment:offset of this windowing function
that may be called directly for this reason. Note that a different
entry point may be returned based upon the selected mode. Therefore,
it is necessary to retrieve this segment:offset specifically for each
desired mode.
Input: AX = 4F05h VBE Display Window Control
BH = 00h Set memory window
= 01h Get memory window
BL = Window number
= 00h Window A
= 01h Window B
DX = Window number in video memory in window
granularity units (Set Memory Window only)
Output: AX = VBE Return Status
DX = Window number in window granularity units
(Get Memory Window only)
Note: In VBE 1.2 implementations, the direct far call version returns
no Return Status information to the application. Also, in the far call
version, the AX and DX registers will be destroyed. Therefore if AX
and/or DX must be preserved, the application must do so prior to
making the far call. The application must still load the input
arguments in BH, BL, and DX (for Set Window). In VBE 2.0
implementations, the BIOS will return the correct Return Status, and
therefore the application must assume that AX and DX will be
destroyed.
Application Developer's Note: This function is not intended for use
in a linear frame buffer mode, if this function is requested, the
function call will fail with the VBE Completion code AH=03h.
VBE BIOS Implementation Note: If this function is called while in a
linear frame buffer memory model, this function must fail with
completion code AH=03h.
4.9. Function 06h - Set/Get Logical Scan Line Length
This required function sets or gets the length of a logical scan line.
This allows an application to set up a logical display memory buffer
that is wider than the displayed area. VBE Function 07h (Set/Get
Display Start) then allows the application to set the starting
position that is to be displayed.
Input: AX = 4F06h VBE Set/Get Logical Scan Line Length
BL = 00h Set Scan Line Length in Pixels
= 01h Get Scan Line Length
= 02h Set Scan Line Length in Bytes
= 03h Get Maximum Scan Line Length
CX = If BL=00h Desired Width in Pixels
If BL=02h Desired Width in Bytes
(Ignored for Get Functions)
Output: AX = VBE Return Status
BX = Bytes Per Scan Line
CX = Actual Pixels Per Scan Line
(truncated to nearest complete pixel)
DX = Maximum Number of Scan Lines
Note: The desired width in pixels or bytes may not be achievable
because of hardware considerations. The next larger value will be
selected that will accommodate the desired number of pixels or bytes,
and the actual number of pixels will be returned in CX. BX returns a
value that when added to a pointer into display memory will point to
the next scan line. For example, in VGA mode 13h this would be 320,
but in mode 12h this would be 80. DX returns the number of logical
scan lines based upon the new scan line length and the total memory
installed and usable in this display mode.
Note: This function is also valid in text modes. In text modes the
application should convert the character line length to pixel line
length by getting the current character cell width through the
XCharSize field returned in ModeInfoBlock, multiplying that times the
desired number of characters per line, and passing that value in the
CX register. In addition, this function will only work if the line
length is specified in character granularity. i.e. in 8 dot modes
only multiples of 8 will work. Any value which is not in character
granularity will result in a function call failure.
Note: On a failure to set scan line length by setting a CX value too
large, the function will fail with error code 02h.
Note: The value returned when BL=03h is the lesser of either the
maximum line length that the hardware can support, or the longest scan
line length that would support the number of lines in the current
video mode.
4.10. Function 07h - Set/Get Display Start
This required function selects the pixel to be displayed in the upper
left corner of the display. This function can be used to pan and
scroll around logical screens that are larger than the displayed
screen. This function can also be used to rapidly switch between two
different displayed screens for double buffered animation effects.
Input: AX = 4F07h VBE Set/Get Display Start Control
BH = 00h Reserved and must be 00h
BL = 00h Set Display Start
= 01h Get Display Start
= 80h Set Display Start during Vertical
Retrace
CX = First Displayed Pixel In Scan Line
(Set Display Start only)
DX = First Displayed Scan Line (Set Display Start
only)
Output: AX = VBE Return Status
BH = 00h Reserved and will be 0 (Get Display Start
only)
CX = First Displayed Pixel In Scan Line (Get Display
Start only)
DX = First Displayed Scan Line (Get Display
Start only)
Note: This function is also valid in text modes. To use this
function in text mode, the application should convert the character
coordinates to pixel coordinates by using XCharSize and YCharSize
returned in the ModeInfoBlock. If the requested Display Start
coordinates do not allow for a full page of video memory or the
hardware does not support memory wrapping, the Function call should
fail and no changes should be made. As a general case, if a requested
Display Start is not available, fail the Function call and make no
changes.
4.11. Function 08h - Set/Get DAC Palette Format
This required function manipulates the operating mode or format of the
DAC palette. Some DACs are configurable to provide 6 bits, 8 bits, or
more of color definition per red, green, and blue primary colors.
The DAC palette width is assumed to be reset to the standard VGA value
of 6 bits per primary color during any mode set
Input: AX = 4F08h VBE Set/Get Palette Format
BL = 00h Set DAC Palette Format
= 01h Get DAC Palette Format
BH = Desired bits of color per primary
(Set DAC Palette Format only)
Output: AX = VBE Return Status
BH = Current number of bits of color per primary
An application can determine if DAC switching is available by querying
Bit D0 of the Capabilities field of the VbeInfoBlock structure
returned by VBE Function 00h (Return Controller Information). The
application can then attempt to set the DAC palette width to the
desired value. If the display controller hardware is not capable of
selecting the requested palette width, then the next lower value that
the hardware is capable of will be selected. The resulting palette
width is returned.
This function will return failure code AH=03h if called in a direct
color or YUV mode.
4.12. Function 09h - Set/Get Palette Data
This required function is very important for RAMDAC's which are larger
than a standard VGA RAMDAC. The standard INT 10h BIOS Palette
function calls assume standard VGA ports and VGA palette widths. This
function offers a palette interface that is independent of the VGA
assumptions.
Input: AX = 4F09h VBE Load/Unload Palette Data
BL = 00h Set Palette Data
= 01h Get Palette Data
= 02h Set Secondary Palette Data
= 03h Get Secondary Palette Data
= 80h Set Palette Data during Vertical Retrace
with Blank Bit on
CX = Number of palette registers to update
DX = First palette register to update
ES:DI= Table of palette values (see below for
format)
Output: AX = VBE Return Status
Format of Palette Values: Alignment byte, Red byte, Green byte, Blue
byte
Note: The need for BL= 80h is for older style RAMDAC's where
programming the RAM values during display time causes a "snow-like"
effect on the screen. Newer style RAMDAC's don't have this limitation
and can easily be programmed at any time, but older RAMDAC's require
that they be programmed during a non-display time only to stop the
snow like effect seen when changing the DAC values. When this is
requested the VBE implementation will program the DAC with blanking
on. Check D2 of the Capabilities field returned by VBE Function 00h
to determine if 80h should be used instead of 00h.
Note: The need for the secondary palette is for anticipated future
palette extensions, if a secondary palette does not exist in a
implementation and these calls are made, the VBE implementation will
return error code 02h.
Note: When in 6 bit mode, the format of the 6 bits is LSB, this is
done for speed reasons, as the application can typically shift the
data faster than the BIOS can.
Note: All application should assume the DAC is defaulted to 6 bit
mode. The application is responsible for switching the DAC to higher
color modes using Function 08h.
Note: Query VBE Function 08h to determine the RAMDAC width before
loading a new palette.
4.13. Function 0Ah - Return VBE Protected Mode Interface
This required function call returns a pointer to a table that contains
code for a 32-bit protected mode interface that can either be copied
into local 32 bit memory space or can be executed from ROM providing
the calling application sets all required selectors and I/O access
correctly. This function returns a pointer (in real mode space) with
offsets to the code fragments, and additionally returns an offset to a
table which contains Non-VGA Port and Memory locations which an
Application may have to have I/O access to.
Input: AX = 4F0Ah VBE 2.0 Protected Mode Interface
BL = 00h Return protected mode table
Output: AX = Status
ES = Real Mode Segment of Table
DI = Offset of Table
CX = Length of Table including protected mode code
(for copying purposes)
The format of the table is as follows:
ES:DI + 00h Word Offset in table of Protected mode code for
Function 5 for Set Window Call
ES:DI + 02h Word Offset in table of Protected mode code for
Function 7 for set Display Start
ES:DI + 04h Word Offset in table of Protected mode code for
Function 9 for set Primary Palette data
ES:DI + 06h Word Offset in table of Ports and Memory Locations
that the application may need I/O privilege for.
(Optional: if unsupported this must be 00GAh)
(See Sub-table for format)
ES:DI + ? Variable remainder of Table including Code
The format of the Sub-Table (Ports and Memory locations)
Port, Port, ... , Port, Terminate Port List with FF FF, Memory
locations (4 bytes), Length (2 bytes), Terminate Memory List with
FF FF.
Example 1. For Port/Index combination 3DE/Fh and Memory locations
DE800-DEA00h (length = 2A h) the table would look like this:
DE 03 DF 03 FF FF 00 E8 0D 00 00 02 FF FF
Example 2. For only the ports it would look like:
DE 03 DF 03 FF FF FF FF
Example 3. For only the memory locations it would look like
FF FF 00 E8 0D 00 00 02 FF FF
Note:. All protected mode functions should end with a near RET (as
opposed to FAR RET) to allow the application software to CALL the code
from within the ROM.
Note: The Port and Memory location Sub-table does not include the
Frame Buffer Memory location. The Frame Buffer Memory location is
contained within the ModeInfoBlock returned by VBE Function 01h.
Note: The protected mode code is assembled for a 32-bit code segment,
when copying it, the application must copy the code to a 32-bit code
segment.
Note: It is the application's responsibility to ensure that the
selectors and segments are set up correctly.
Note: Currently undefined registers may be destroyed with the
exception of ESI, EBP, DS and SS.
Note: Refer to Section 4.2 for information on protected mode
consideration
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