Intel® 815 Chipset: Graphics Controller PRM, Rev 1.0

R

9.6.28.CR24Test Register for Toggle State of Attribute Controller

Register

I/O (and Memory Offset) Address:

3B5h/3D5h (index=24h)

 

Default:

 

00h

 

Attributes:

 

Read Only

 

7

6

0

 

 

 

Toggle

 

Reserved (0000000)

 

 

 

Status

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Bit

 

Description

 

7Toggle Status. Last write to attribute register was to: 0 = index port

1 = data port

6:0

Reserved. Read as 0s.

9.6.29.CR30Extended Vertical Total Register

I/O (and Memory Offset) Address:

3B5h/3D5h (index=30h)

 

 

Default:

 

00h

 

 

 

Attributes:

Read/Write

 

 

7

 

4

3

0

 

 

 

 

Reserved (0000)

 

Vertical Total Bits 11:8

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Bit

 

 

Description

 

 

 

 

 

 

 

 

7:4

Reserved. Read as 0s. This field must be 0s when this register is written.

 

 

 

 

 

 

3:0

Vertical Total Bits [11:8]. The vertical total is 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 bits [7:0] of the

 

 

 

Vertical Total Register (CR06), and the 2 most significant bits are supplied by bits 5 and 0 of the

 

 

 

 

 

Overflow Register (CR07). In standard VGA modes, these 4 bits of this register are not used.

 

 

 

 

 

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 bits [7:0] of the

 

 

 

Vertical Total Register (CR06), and the 4 most significant bits are supplied by these 4 bits of this

 

 

 

 

 

register.

 

 

 

 

 

 

 

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

 

 

 

 

 

 

 

 

132

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Image 132
Intel 815 manual 29. CR30Extended Vertical Total Register