Intel 815 4. AR11Overscan Color Register, 5. AR12Memory Plane Enable Register, Bit 54 ST01 Bit

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Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0

R

9.4.4.AR11Overscan Color Register

I/O (and Memory Offset) Address:

Read at 3C1h and Write at 3C0h; (index=11h)

Default:

 

UUh (U=Undefined)

Attributes:

Read/Write

 

 

 

 

 

Bit

 

Description

 

 

 

 

7:0

Overscan. These 8 bits select the overscan (border) color. The border color is displayed during the

 

 

blanking intervals. For monochrome displays, this value should be set to 00h.

 

 

 

 

9.4.5.AR12Memory Plane Enable Register

I/O (and Memory Offset) Address: Read at 3C1h and Write at 3C0h; (index=12h)

Default:

 

 

00UU UUUUb (U=Undefined)

 

 

 

 

Attributes:

 

 

Read/Write

 

 

 

 

 

7

 

 

6

5

4

3

2

1

 

0

 

 

 

 

Reserved (00)

 

Video Status Mux

Enable

Enable

Enable

 

Enable

 

 

 

 

 

 

 

 

 

Plane 3

Plane 2

Plane 1

 

Plane 0

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Bit

 

 

 

 

 

Description

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

7:6

 

Reserved. Read as 0s.

 

 

 

 

 

 

 

 

 

 

 

5:4

 

Video Status Mux. These 2 bits are used to select 2 of the 8 possible palette bits (P7-P0) to be made

 

 

 

 

available to be read via bits 5 and 4 of the Input Status Register 1 (ST01). The table below shows the

 

 

 

 

possible choices.

 

 

 

 

 

 

 

 

 

 

 

 

Bit [5:4] ST01 Bit 5

ST01 Bit 4

 

 

 

 

 

 

 

 

 

 

00

P2 (default)

P0 (default)

 

 

 

 

 

 

 

 

 

 

01

P5

 

P4

 

 

 

 

 

 

 

 

 

 

10

P3

 

P1

 

 

 

 

 

 

 

 

 

 

11

P7

 

P6

 

 

 

 

 

 

 

 

 

 

These bits are typically unused by current software; they are provided for EGA compatibility.

 

 

 

 

 

3:0

 

Enable Plane [3:0]. These 4 bits individually enable the use of each of the 4 memory planes in

 

 

 

 

providing 1 of the 4 bits used in video output to select 1 of 16 possible colors from the palette to be

 

 

 

 

displayed.

 

 

 

 

 

 

 

 

 

 

 

 

0 = Disable the use of the corresponding memory plane in video output to select colors, forcing the bit

 

 

 

 

that the corresponding memory plane would have provided to a value of 0.

 

 

 

 

 

 

1 = Enable the use of the corresponding memory plane in video output to select colors.

 

 

 

 

 

 

Note:

 

 

 

 

 

 

 

 

 

 

 

 

 

AR12 is referred to in the VGA standard as the Color Plane Enable Register. The words “plane,” “color

 

 

 

 

plane,” “display memory plane,” and “memory map” have been all been used in IBM literature on the

 

 

 

 

VGA standard to describe the 4 separate regions in the frame buffer that are amongst which pixel color

 

 

 

 

or attributes information is split up and stored in standard VGA planar modes. This use of multiple terms

 

 

 

 

for the same subject was considered confusing; therefore, AR12 is called the Memory Plane Enable

 

 

 

 

Register.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Page 104
Image 104
Intel 815 manual 4. AR11Overscan Color Register, 5. AR12Memory Plane Enable Register, Bit 54 ST01 Bit