AD9974BBCZ datasheet(20/52 Pages) AD

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AD9974

Rev. A | Page 20 of 52

Individual HBLK Patterns

The HBLK programmable timing shown in Figure 25 is similar

to CLPOB and PBLK; however, there is no start polarity control.

Only the toggle positions designate the start and the stop positions

of the blanking period. Additionally, as shown in Figure 26, there

is a polarity control, HBLKMASK, for H1/H3 and H2/H4 that

designates the polarity of the horizontal clock signals during the

blanking period. Setting HBLKMASK_H1 low sets H1 = H3 =

low and HBLKMASK_H2 high sets H2 = H4 = high during the

blanking. As with the CLPOB and PBLK signals, HBLK registers

are available in each H-pattern group, allowing unique blanking

signals to be used with different vertical timing sequences.

The AD9974 supports three modes of HBLK operation. HBLK

Mode 0 supports basic operation and provides some support for

special HBLK patterns. HBLK Mode 1 supports pixel mixing

HBLK operation. HBLK Mode 2 supports advanced HBLK opera-

tion. The following sections describe each mode. Register

parameters are detailed 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 27.

The pattern in this example uses all six toggle positions to generate

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

the toggle positions, different patterns are created.

Separate toggle positions are available for even and odd lines.

If alternation is not needed, load the same values into the registers

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

HBLK

SPECIAL H-BLANK PATTERN IS CREATED USING MULTIPLE HBLK TOGGLE POSITIONS (HBLKALT = 0).

H1/H3

H2/H4

HBLKTOGE1

HBLKTOGE2

HBLKTOGE3

HBLKTOGE4

HBLKTOGE5

HBLKTOGE6

Figure 27. Generating Special HBLK Patterns

Table 12. HBLK Pattern Registers

Length (Bits)

Range

Description

HBLK_MODE

0 to 2 HBLK modes

Enables different HBLK toggle position operations.

0 = normal mode. Six toggle positions available for even and odd lines.

If even/odd alternation is not needed, set toggles for even/odd the same.

1 = pixel mixing mode. In addition to six toggle positions, the HBLKSTART,

HBLKEND, HBLKLEN, and HBLKREP registers can be used to generate HBLK

patterns. If even/odd alternation is not needed, set toggles for even/odd

the same.

2 = advanced HBLK mode. Divides HBLK interval into six different repeat

areas. Uses HBLKSTARTA/B/C and RA*H*REPA/B/C registers.

3 = test mode only. Do not access.

HBLKSTART

0 to 8191 pixel location

Start location for HBLK in HBLK Mode 1 and HBLK Mode 2.

HBLKEND

0 to 8191 pixel location

End location for HBLK in HBLK Mode 1 and HBLK Mode 2.

HBLKLEN

0 to 8191 pixels

HBLK length in HBLK Mode 1 and HBLK Mode 2.

HBLKREP

0 to 8191 repetitions

Number of HBLK repetitions in HBLK Mode 1 and HBLK Mode 2.

HBLKMASK_H1

High/low

Masking polarity for H1 and H3 during HBLK.

HBLKMASK_H2

High/low

Masking polarity for H2 and H4 during HBLK.

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