User's Manual

Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0

9.3.8. GR06



Miscellaneous 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

Odd/Even

Graphics /

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.