Intel 815 manual Sequencer Registers, SRXSequencer Index

Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0

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Table 8.	CRT Display Sync Polarities
	V	H	Display	Horizontal	Vertical Frequency
				Frequency
	P	P	>480 Line	Variable	Variable
	P	P	200 Line	15.7 KHz	60 Hz
	N	P	350 Line	21.8 KHz	60 Hz
	P	N	400 Line	31.5 KHz	70 Hz
	N	N	480 Line	31.5 KHz	60 Hz

9.2.Sequencer Registers

The sequencer registers are accessed via either I/O space or Memory space. To access the registers the VGA Sequencer Index register (SRX) at I/O address 3C4h (or memory address 3C4h) is written with the index of the desired register. Then the desired register is accessed through the data port for the sequencer registers at I/O address 3C5 (or memory address 3C5).

9.2.1.SRXSequencer Index

I/O (and Memory Offset) Address: 3C4h

Default:00h

Attributes:Read/Write

7	3	2	0
	Reserved (00000)		Sequencer Index
Bit	Descriptions
7:3	Reserved. Read as 0s.
2:0	Sequencer Index. This field contains a 3-bit Sequencer Index value used to access sequencer data re-
	gisters at indices 0 through 7.
	Notes:

1.SR02 is referred to in the VGA standard as the Map Mask Register. However, the word “map” is used with multiple meanings in the VGA standard and was, therefore, deemed too confusing; hence, the reason for calling it the Plane Mask Register.

2.SR07 is a standard VGA register that was not documented by IBM. It is not an graphics controller extension.

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