Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0

R

9.3.8.GR06Miscellaneous Register

I/O (and Memory Offset) Address: 3CFh (Index=06h)

 

 

 

Default:

 

0Uh (U=Undefined)

 

 

 

Attributes:

Read/Write

 

 

 

 

7

 

4

 

3

2

1

0

 

 

 

 

 

Reserved (0000)

 

 

Memory Map Mode

Chain

Graphics /

 

 

 

 

 

 

 

 

 

Odd/Even

Text

 

 

 

 

 

 

 

 

 

 

Mode

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Bit

 

 

 

Description

 

 

 

 

 

 

 

 

 

 

 

 

7:4

Reserved. Read as 0s.

 

 

 

 

 

 

 

 

 

3:2

Memory Map Mode. These 2 bits control the mapping of the frame buffer into the processor address

 

 

 

space as follows:

 

 

 

 

 

 

 

 

Bit [3:2]

Frame Buffer Address Range

 

 

 

 

 

 

 

 

00

A0000h BFFFFh

 

 

 

 

 

 

 

 

01

A0000h AFFFFh

 

 

 

 

 

 

 

 

10

B0000h B7FFFh

 

 

 

 

 

 

 

 

11

B8000h BFFFFh

 

 

 

 

 

 

 

 

Notes:

 

 

 

 

 

 

 

 

 

 

1. This function is both in standard VGA modes and in extended modes that do not provide linear frame

 

 

 

buffer access.

 

 

 

 

 

 

 

 

2. Software must set to the proper value.

 

 

 

 

 

 

 

 

 

1

Chain Odd/Even. This bit provides the ability to alter the interpretation of address bit A0, so that it may

 

 

 

be used in selecting between the odd-numbered memory planes (planes 1 and 3) and the even-

 

 

 

numbered memory planes (planes 0 and 2).

 

 

 

 

 

 

 

 

0 = A0 functions normally.

 

 

 

 

 

 

 

 

1 = A0 is switched with a high order address bit, in terms of how it is used in address decoding. The

 

 

 

result is that A0 is used to determine which memory plane is being accessed

 

 

 

 

 

(A0=0 for planes 0 and 2 and A0=1 for planes 1 and 3).

 

 

 

 

 

 

 

 

 

 

 

 

0

Graphics/Text Mode.

 

 

 

 

 

 

 

 

0 = Text mode.

 

 

 

 

 

 

 

 

1 = Graphics mode.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

96

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Image 96
Intel 815 manual 8. GR06Miscellaneous Register, Bit, Graphics/Text Mode