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AD9991

–14–

HBLK

PROGRAMMABLE SETTINGS:

1. FIRST TOGGLE POSITION = START OF BLANKING

2. SECOND TOGGLE POSITION = END OF BLANKING

BLANK

Figure 10. Horizontal Blanking (HBLK) Pulse Placement

HBLK

THE POLARITY OF H1 DURING BLANKING IS PROGRAMMABLE (H2 IS OPPOSITE POLARITY OF H1).

H1/H3

H2/H4

Figure 11. HBLK Masking Control

HBLK

SPECIAL H-BLANK PATTERN IS CREATED USING MULTIPLE HBLK TOGGLE POSITIONS

H1/H3

H2/H4

TOG1

TOG2

TOG3

TOG4

TOG5

TOG6

Figure 12. Generating Special HBLK Patterns

Generating Special HBLK Patterns

There are six toggle positions available for HBLK. Normally,

only two of the toggle positions are used to generate the standard

HBLK interval. However, the additional toggle positions may be

used to generate special HBLK patterns, as shown in Figure 12.

The pattern in this example uses all six toggle positions to gen-

erate two extra groups of pulses during the HBLK interval. By

changing the toggle positions, different patterns can be created.

Generating HBLK Line Alternation

One further feature of the AD9991 is the ability to alternate dif-

ferent HBLK toggle positions on odd and even lines. This may be

used in conjunction with V-pattern odd/even alternation or on its

own. When a 1 is written to the HBLKALT register, TOG1 and

TOG2 are used on odd lines only, while TOG3–TOG6 are used

on even lines. Writing a 2 to the HBLKALT register gives the

opposite result: TOG1 and TOG2 are used on even lines, while

TOG3–TOG6 are used on odd lines. See the Vertical Timing

Generation, Line Alternation section for more information.

REV. 0

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