AD9920ABBCZ datasheet(24/112 Pages) AD

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AD9920A

Rev. B | Page 24 of 112

CLPOB

PBLK

PROGRAMMABLE SETTINGS:

1START POLARITY (CLAMP AND BLANK REGION ARE ACTIVE LOW).

2FIRST TOGGLE POSITION.

3SECOND TOGGLE POSITION.

ACTIVE

Figure 27. Clamp and Preblank Pulse Placement

NO CLPOB SIGNAL

FOR LINE 600

NO CLPOB SIGNAL

FOR LINES 6 TO 8

CLPMASKSTART1 = 6

CLPMASKEND1 = 9

597

598

CLPMASKSTART2 = 600

CLPMASKEND2 = 601

CLPOB

Figure 28. CLPOB Masking Example

Individual HBLK Patterns

The HBLK programmable timing shown in Figure 29 is similar to

the timing of CLPOB and PBLK; however, there is no start polarity

control. Only the toggle positions are used to designate the start

and stop positions of the blanking period. Additionally, separate

masking polarity controls for each H-clock phase designate the

polarity of the horizontal clock signals during the blanking period.

Setting HBLKMASK_H1 high sets H1—and, therefore, H3, H5,

and H7—low during the blanking, as shown in Figure 30. As with

the CLPOB and PBLK signals, HBLK registers are available in

each V-sequence, allowing different blanking signals to be used

with different vertical timing sequences.

The AD9920A supports two modes of HBLK operation. HBLK

Mode 0 supports basic operation and pixel mixing HBLK oper-

ation. HBLK Mode 1 supports advanced HBLK operation.

The following sections describe each mode in detail. Register

parameters are described in detail in Table 12.

HBLK Mode 0 Operation

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 can be

used to generate special HBLK patterns, as shown in Figure 31.

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.

Separate toggle positions are available for even and odd lines. If

alternation is not needed, the same values should be loaded into

the registers for even (HBLKTOGE) and odd (HBLKTOGO) lines.

Multiple repeats of the HBLK signal are enabled by setting the

HBLKLEN and HBLKREP registers along with the six toggle

positions (four are shown in Figure 32).

Generating HBLK Line Alternation

HBLK Mode 0 provides the ability to alternate different HBLK

toggle positions on even and odd lines. HBLK line alternation

can be used alone or in conjunction with V-pattern odd/even

alternation (see the Generating Line Alternation for V-Sequences

and HBLK section). Separate toggle positions are available for

even and odd lines. If even/odd line alternation is not needed,

the same values should be loaded into the registers for even

(HBLKTOGE) and odd (HBLKTOGO) lines.

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