AD9974BBCZ datasheet(24/52 Pages) AD

24 / 52 page

AD9974

Rev. A | Page 24 of 52

HBLK, PBLK, and CLPOB Toggle Positions

The AD9974 uses an internal horizontal pixel counter to position

the HBLK, PBLK, and CLPOB toggle positions. The horizontal

counter does not reset to 0 until 12 CLI periods after the falling

edge of HD. This 12-cycle pipeline delay must be considered

when determining the register toggle positions. For example, if

CLPOB_TOG1 is 100 and the pipeline delay is not considered,

the final toggle position is applied at 112. To obtain the correct

toggle positions, the toggle position registers must be set to the

desired toggle position minus 12.

For example, if the desired toggle position is 100, CLPOB_TOG

should be set to 88 (that is, 100 − 12). Figure 49 shows the 12-cycle

pipeline delay referenced to the falling edge of HD.

Caution

Toggle positions cannot be programmed during the 12-cycle

delay from the HD falling edge until the H-counter has reset.

See Figure 33 for an example of this restriction.

1. HBLKTOG1

(60 – 12) = 48

2. HBLKTOG2

100

(100 – 12) = 88

3. CLPOB_TOG1

103

(103 – 12) = 91

4. CLPOB_TOG2

112

(112 – 12) = 100

DESIRED

TOGGLE

POSITION

ACTUAL

VALUE

CLPOB

PIXEL NO.

112

103

100

Figure 32. Example of Register Setting to Obtain Desired Toggle Positions

NO TOGGLE POSITIONS ALLOWED IN THIS AREA

NOTES

1. TOGGLE POSITIONS CANNOT BE PROGRAMMED WITHIN 12 PIXELS OF PIXEL 0 LOCATION.

H-COUNTER

(PIXEL COUNTER)

N-1

N-2

N-3

N-4

N-5

N-6

N-7

N-8

N-9

N-10

N-11

N-12

H-COUNTER

RESET

Figure 33. Restriction for Toggle Position Placement

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