Intel 815 manual 5. SR03Character Font, Bit 32 Map Number Table Location

Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0

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9.2.5.SR03Character Font

I/O (and Memory Offset) Address:							3C5h (index=03h)
Default:							00h
Attributes:							Read/Write
7					6	5	4	3		2	1	0
			Reserved (00)			Char Map	Char Map		Character Map A Select		Character Map B Select
						A Select	B Select		(bits 2 and 1)		(bits 2 and 1)
						(bit 0)	(bit 0)
		Bit						Descriptions
	7:6			Reserved. Read as 0s.
	3:2,5			Character Map Select Bits for Character Map B. These three bits are used to select the character
				map (character generator tables) to be used as the secondary character set (font). Note that the
				numbering of the maps is not sequential.
				Bit [3:2, 5]	Map Number		Table Location
				00,0	0		1st 8KB of plane 2 at offset 0 (default)
				00,1	4		2nd 8KB of plane 2 at offset 8K
				01,0	1		3rd 8KB of plane 2 at offset 16K
				01,1	5		4th 8KB of plane 2 at offset 24K
				10,0	2		5th 8KB of plane 2 at offset 32K
				10,1	6		6th 8KB of plane 2 at offset 40K
				11,0	3		7th 8KB of plane 2 at offset 48K
				11,1	7		8th 8KB of plane 2 at offset 56K
	1:0,4			Character Map Select Bits for Character Map A. These three bits are used to select the character
				map (character generator tables) to be used as the primary character set (font). Note that the
				numbering of the maps is not sequential.
				Bit [1:0,4]	Map Number		Table Location
				0,00	0		1st 8KB of plane 2 at offset 0 (default)
				0,01	4		2nd 8KB of plane 2 at offset 8K
				0,10	1		3rd 8KB of plane 2 at offset 16K
				0,11	5		4th 8KB of plane 2 at offset 24K
				1,00	2		5th 8KB of plane 2 at offset 32K
				1,01	6		6th 8KB of plane 2 at offset 40K
				1,10	3		7th 8KB of plane 2 at offset 48K
				1,11	7		8th 8KB of plane 2 at offset 56K
	NOTES:

1.In text modes, bit 3 of the video data’s attribute byte normally controls the foreground intensity. This bit may be redefined to control switching between character sets. This latter function is enabled whenever there is a difference in the values of the Character Font Select A and the Character Font Select B bits. If the two values are the same, the character select function is disabled and attribute bit 3 controls the foreground intensity.

2.Bit 1 of the Memory Mode Register (SR04) must be set to 1 for the character font select function of this register to be active. Otherwise, only character maps 0 and 4 are available.

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