Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0

R

9.6.8.CR06Vertical Total Register

I/O (and Memory Offset) Address:

3B5h/3D5h (index=06h)

Default:

 

00h

Attributes:

Read/Write (Group 0 Protection)

 

 

 

 

 

Bit

 

Description

 

 

 

 

7:0

Vertical Total Bits [7:0]. This field provides the 8 least significant bits of either a 10-bit or 12-bit value

 

 

that specifies the total number of scan lines. This includes the scan lines both inside and outside of the

 

 

active display area.

 

 

 

In standard VGA modes, where bit 0 of the I/O Control Register (CR80) is set to 0, the vertical total is

 

 

specified with a 10-bit value. The 8 least significant bits of this value are supplied by these 8 bits of this

 

 

register, and the 2 most significant bits are supplied by bits 5 and 0 of the Overflow Register (CR07).

 

 

In extended modes, where bit 0 of the I/O Control Register (CR80) is set to 1, the vertical total is

 

 

specified with a 12-bit value. The 8 least significant bits of this value are supplied by these 8 bits of this

 

 

register, and the 4 most significant bits are supplied by bits [3:0] of the Extended Vertical Total Register

 

 

(CR30).

 

 

 

This 10-bit or 12-bit value should be programmed to equal the total number of scan lines, minus 2.

 

 

 

 

9.6.9.CR07Overflow Register

I/O (and Memory Offset) Address:

3B5h/3D5h (index=07h)

 

 

 

Default:

 

 

 

UU0U UUU0b (U=Undefined)

 

 

 

Attributes:

 

 

Read/Write (Group 0 Protection on bits [7:5, 3:0])

7

 

6

5

4

3

2

1

0

 

 

 

Vert Sync

Vert Disp

Vert Total

Line Cmp

Vert Blnk

Vert Sync

Vert Disp

Vert Total

 

 

 

Start Bit 9

En Bit 9

Bit 9

Bit 8

Start Bit 8

Start Bit 8

En Bit 8

Bit 8

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Bit

 

 

 

 

Description

 

 

 

 

 

 

 

 

7

Vertical Sync Start Bit 9. The vertical sync start is a 10-bit or 12-bit value that specifies the beginning

 

 

 

of the vertical sync pulse relative to the beginning of the active display area.

 

 

 

 

 

In standard VGA modes, where bit 0 of the I/O Control Register (CR80) is set to 0, the vertical sync start

 

 

 

is specified with a 10-bit value. The 8 least significant bits of this value are supplied by bits [7:0] of the

 

 

 

Vertical Sync Start Register (CR10), and the most and second-most significant bits are supplied by this

 

 

 

bit and bit 2, respectively, of this register.

 

 

 

 

 

 

 

 

In extended modes, where bit 0 of the I/O Control Register (CR80) is set to 1, the vertical display end is

 

 

 

specified with a 12-bit value. The 8 least significant bits of this value are supplied by bits [7:0] of the

 

 

 

Vertical Sync Start Register (CR10), and the 4 most significant bits are supplied by bits [3:0] of the

 

 

 

Extended Vertical Sync Start Register (CR32) register. In extended modes, neither this bit, nor bit 2 of

 

 

 

this register are used.

 

 

 

 

 

 

 

 

 

This 10-bit or 12-bit value should be programmed to be equal to the number of scan lines from the

 

 

 

beginning of the active display area to the start of the vertical sync pulse. Since the active display area

 

 

 

always starts on the 0th scan line, this number should be equal to the number of the scan line on which

 

 

 

the vertical sync pulse begins.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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Intel 815 manual 8. CR06Vertical Total Register, 9. CR07Overflow Register