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AD9949

Rev. B | Page 23 of 36

GENERATING SPECIAL HBLK PATTERNS

Six toggle positions are 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 24. 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 can be created.

HORIZONTAL SEQUENCE CONTROL

The AD9949 uses sequence change positions (SCP) and

sequence pointers (SPTR) to organize the individual horizontal

sequences. Up to four SCPs are available to divide the readout

into four separate regions, as shown in Figure 25. The SCP0 is

always hard-coded to Line 0, and SCP1 to SCP3 are register

programmable. During each region bounded by the SCP, the

SPTR registers designate which sequence is used by each signal.

CLPOB, PBLK, and HBLK each have a separate set of SCPs. For

example, CLPOBSCP1 defines Region 0 for CLPOB, and in that

region any of the four individual CLPOB sequences may be

selected with the CLPOBSPTR register. The next SCP defines a

new region and in that region, each signal can be assigned to a

different individual sequence. The sequence control registers

are summarized in Table 20.

EXTERNAL HBLK SIGNAL

The AD9949 can also be used with an external HBLK signal.

Setting the HBLKDIR register (Address 0×40) to high disables

the internal HBLK signal generation. The polarity of the exter-

nal signal is specified using the HBLKPOL register, and the

masking polarity of H1 is specified using the HBLKMASK

external HBLK signal.

UP TO FOUR INDIVIDUAL HORIZONTAL CLAMP AND BLANKING REGIONS MAY BE

PROGRAMMED WITHIN A SINGLE FIELD, USING THE SEQUENCE CHANGE POSITIONS.

SEQUENCE CHANGE OF POSITION 1

SEQUENCE CHANGE OF POSITION 2

SEQUENCE CHANGE OF POSITION 3

SINGLE FIELD (1 VD INTERVAL)

CLAMP AND PBLK SEQUENCE REGION 0

SEQUENCE CHANGE OF POSITION 0

(V-COUNTER = 0)

CLAMP AND PBLK SEQUENCE REGION 3

CLAMP AND PBLK SEQUENCE REGION 2

CLAMP AND PBLK SEQUENCE REGION 1

Figure 25. Clamp and Blanking Sequence Flexibility

Table 21. External HBLK Register Parameters

Length

Range

Description

HBLKDIR

High/Low

Specifies HBLK Internally Generated or Externally Supplied.

1 = External.

HBLKPOL

High/Low

External HBLK Active Polarity.

0 = Active Low.

1 = Active High.

HBLKEXTMASK

High/Low

External HBLK Masking Polarity.

0 = Mask H1 Low.

1 = Mask H1 High.

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