B69000 Asiliant Technologies, B69000 Datasheet - Page 88

• Manufacturer Part Number: B69000
• Manufacturer: Asiliant Technologies

Specifications of B69000

• Lead Free Status / Rohs Status: Supplier Unconfirmed

8-2
ST00
read-only at I/O Address 3C2h
7
Note:
6-5
4
3-0
&+,36
Interrupt
Vert Ret
7
Vertical Retrace Interrupt
0: Indicates that a vertical retrace interrupt is not pending.
1: Indicates that a vertical retrace interrupt is pending.
This bit does NOT indicate the status of any real hardware interrupt occurring at the onset of vertical
retrace. This bit works in conjunction with bit 3 of ST01 and bits 4 and 5 of CR11 to implement a
“phantom” interrupt for the sake of compatibility with older software. Early VGA graphics systems
(and their predecessors, including the EGA) had the ability to generate a hardware interrupt on
IRQ9 whenever a vertical retrace commenced. This was done because in these earlier graphics
systems it was important for the host CPU to wait for a vertical retrace interval before accessing the
frame buffer. If the host CPU accessed the frame buffer at a time other than the vertical retrace
interval, i.e., while data for the active display area was being drawn to the display, then either “snow”
on the display or a flickering display would result. Later graphics systems, including this one, do
NOT actually generate this interrupt.
Reserved
These bits return the value of 0 when read.
DAC CRT Sense
Indicates the state of the DAC analog output comparators. The comparators can be used to
determine whether a CRT is currently attached, and/or whether the CRT is color or monochrome.
This is done by blanking the CRT outputs, which causes the color value stored at index 0 in the
color lookup table of the RAMDAC to be continuously output to the CRT. Different color values can
then be written to the color lookup table at index 0 to set different output levels for the red, green
and blue D-to-A converters.
Reserved
These bits return the value of 0 when read.
69000 Databook
Input Status Register 0
Result
6
0
1
Reserved
When Testing for Presence of CRT
5
General Control and Status Registers
Subject to Change Without Notice
No CRT is present.
CRT is present.
DAC CRT
Sense
4
3
2
When Testing for Color or
Reserved
Monochrome CRT
Monochrome CRT.
Color CRT.
Revision 1.3 8/31/98
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