M69000 Asiliant Technologies, M69000 Datasheet - Page 322

• Manufacturer Part Number: M69000
• Manufacturer: Asiliant Technologies

Specifications of M69000

• Lead Free Status / Rohs Status: Supplier Unconfirmed

Horizontal and Vertical Clocking
Clocking within a horizontal scan line is generally programmed in units of 8 DCLK cycles (8 pixels), often
referred to as “character” clocks (for graphics modes as well as text modes). The “character” clocks are
numbered from 0 to n-1, where “n” is the total number of character clocks per horizontal scan (including
blanking and border intervals as well as the “addressable video” interval). Character clock #0 corresponds
to the start of the “addressable video” interval, also known as the “Display Enable” interval. Starting at
character clock #0, the following horizontal timing events occur:
Similarly, vertical clocking is generally programmed in units of scan lines, numbered from 0 to m-1, where
“m” is the total number of scan lines per complete frame and “0” corresponds to the first scan line containing
addressable video information. Starting at scan line #0, the following vertical timing events occur:
Vertical timing can also be “interlaced,” meaning that even numbered scan lines are displayed during one
vertical sweep and odd numbered lines are displayed during the next vertical sweep. This allows more time
(two vertical sweeps instead of one) to display a complete frame, which reduces video bandwidth
requirements while preserving a reasonably flicker-free image. North American television standards use a
60 Hz vertical sync frequency, interlaced for a 30 Hz effective frame rate, with 525 scan lines total per frame
(even lines plus odd, including blanking). The horizontal sync frequency is 525 x 30 Hz = 15.75 KHz.
To achieve interlacing, the sweep of odd-numbered lines is offset by half of a scan line relative to the sweep
of even-numbered lines. The vertical sync pulse for alternate frames occurs in the middle of a scan line
interval (during vertical blanking) instead of at the end. North American television standards sweep 262.5
scan lines on each vertical sweep (60Hz). Each scan line remains full length, but the vertical sync for alter-
nating frames occurs at the middle of the scan line. In the 69000, a CHIPS Super VGA extension register
allows the exact placement of the half-line vertical sync pulse to be programmable, for optimum centering
of odd scan lines between adjacent even scan lines.
Computer CRT displays generally need about 25% of the horizontal total for horizontal border and blanking
intervals, and at least 5% of the vertical total for vertical border and blanking. Flat panels typically can
operate with smaller margins for these “non-addressable” intervals.
&+,36
End of Display Enable
Start of horizontal blanking (end of right border)
Horizontal sync pulse start and end
End of horizontal blanking
Start of left border (This border area is actually for the next physical scan line.)
End of left border area and start of Display Enable (This corresponds to the “Horizontal Total”
parameter.)
End of addressable video
Start of vertical blanking (end of bottom border)
Vertical sync pulse start and end
End of vertical blanking (start of top border) (This border area is actually for the next physical
frame.)
End of top border area and start of addressable video. This corresponds to the “Vertical Total”
parameter.
69000 Databook
Subject to Change Without Notice
Clock Generation
Revision 1.3 8/31/98
B-9