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MX86251

3D graphic chipset

Macronix International 

MX86251

2.2 64-bit Graphics Co-processor

Pattern Map Buffer

The MX86251 Graphics Co-processor accelerates com-

mon Graphics User Interface drawing functions , includ-

ing Bitblt, Rectangle Fill, Pattern Fill, Bresenham Line

Draw, and Text Transfer. Hardware clipping and hardware

cursor further reduce software driver overhead, includ-

ing Bitblt, Rectangle Fill, Pattern Fill, Bresenham Line

Draw, and Text Transfer. Hardware clipping and hardware

cursor further reduce software driver overhead to the

minimum.

The Graphics Co-processor supports scrardware cursor

further rr further reduce software driver overhead to the

minimum.

The Graphics Co-processor supports screen widths of

640, 800, 1024, 1152, 1280, 1600 and 2048. Pixel depth

can be 8, 16, and 32 bits. The display memory size can

be 1,2 or 4 megabytes. All Co-processor drawing opera-

tions are programmed with 32 bit registers in a linear

address aperture.

Three Operand Bitblt

The Graphics Co-processor executes Bitblt operations

between three operands: the Source bitmap, the Desti-

nation bitmap, and the Pattern bitmap. There are 256

operations on bitmaps, called Raster Operations (ROP).

An ALU with three operand inputs is implemented to ex-

ecute any of the 256 RO P ’s in a single cycle, unlike ear-

lier generation GUI chips which used only two operands

and implemented only 16 ROPs. This forced the soft-

ware driver to decompose those 3-operand bitblt into

two or three 2-operand BitBLTs significantly slowing down

the drawing process.

Source/Destination FIFOs

The most common Bitblt operation in Windows is the

PatBlt which means painting a large window background

using a brush which is an 8 by 8 pattern bitmap. Many

GUI chips store the brush pattern bitmap in offscreen

memory. During Patblt, the pattern are fetched repeat-

edly.

To accelerate Patblt, the MX86251 has on-chip memory

to store a full 8 by 8 pattern bitmap. Unlike others which

can only store 8-bit pixels, The MX86251 can store pixel

maps of 8, 16, and 32 bit pixels. This complete imple-

mentation of Pattern Map, enables the MX86251 to ex-

ecute the Patblts at peak memory bandwidth using a long

burst of page mode writes and thus achieving the best

drawing performance.

Text / Font drawing acceleration

Drawing text characters or fonts are another very com-

mon Windows drawing operation. The fonts are mono-

chrome bitmaps that get expanded into color pixel maps

in the Graphics Co-processor. The MX86251 optimizes

this process in several ways.

Font bitmaps can be stored in system memory and trans-

ferred to the Co-processor for color expansion.The

MX86251 provides a screen port to facilitate this memory

to screen transfer. The screen port is mapped in a linear

address aperture of 64K bytes. The monochrome font

pixels are buffered in the Source FIFO so that concur-

rent operations are enabled for font transfer from system

memory and color expansion in the Co-processor. The

display driver can also cache font bitmaps in offscreen

memory using the so called font-cache scheme. The

MX86251 provides direct support of offscreen packed

monochrome bitmap to color map expansion. This op-

eration greatly accelerates the performance of font cache.

The three inputs to the Bitblt ALU are from the Source

FIFO, the Destination FIFO and the Pattern Map Buffer.

The Source and Destination FIFO are 64 bit wide and 8

levels deep. They allow the fetch cycles for Source and

Destination pixels to be run in page mode cycles. By hav-

ing Destination FIFO, the MX86251 can run Destination

read-modify-write operations in page mode reads followed

by page mode writes which is substantially faster than

the read-modify-write cycles in an EDO-DRAM based

system.

Windows 95 Direct Draw acceleration

Windows 95 Direct Draw is aimed to turn the Windows

GUI environment into a Game platform with high speed

sprite animation. The key to sprite animation is Transpar-

ent Blt. The MX86251 implements a flexible Color Key

mechanism to enable high speed Transparent Blt. A Trans-

parent Blt writes to screen a source bitmap, that is, a

sprite, which is in an irregular shape such as a cartoon

figure. The background pixels which should not be over-

written are coded in the special Key color. The Color Com-

P/N:PM0476

REV. 1.2 , FEB 11, 1998

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