AD9848AKST datasheet(21/32 Pages) AD

21 / 32 page

REV. A

–21–

AD9848/AD9849

H2 = H4 = high during the blanking, as shown in Figure 11.

Up to four individual sequences are available for HBLK.

Horizontal Sequence Control

The AD9848/AD9849 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 12.

The SCP 0 is always hard-coded to line 0, and SCP1–3 are

SCP, the SPTR registers designate which sequence is used by

each signal. CLPOB, CLPDM, PBLK, and HBLK each have a

separate set of SCP. For example, CLPOBSCP1 will define Region

0 for CLPOB, and in that region any of the four individual

CLPOB sequences may be selected with the CLPOBSPTR

registers. 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 VI.

(3)

(2)

(1)

CLPOB

CLPDM

PBLK

. . .

NOTES

PROGRAMMABLE SETTINGS:

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

(2) FIRST TOGGLE POSITION

(3) SECOND TOGGLE POSITION

CLAMP

Figure 9. Clamp and Preblank Pulse Placement

(2)

(1)

HBLK

. . .

NOTES

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

Individual CLPOB, CLPDM, PBLK Sequences

The AFE horizontal timing consists of CLPOB, CLPDM, and

PBLK, as shown in Figure 9. These three signals are indepen-

dently programmed using the registers in Table IV. SPOL is the

start polarity for the signal, and TOG1 and TOG2 are the first

and second toggle positions of the pulse. All three signals are

active low and should be programmed accordingly. Up to four

individual sequences can be created for each signal.

Individual HBLK Sequences

The HBLK programmable timing shown in Figure 10 is similar to

CLPOB, CLPDM, and PBLK. However, there is no start polar-

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

start and the stop positions of the blanking period. Additionally,

there is a polarity control HBLKMASK that designates the

polarity of the horizontal clock signals H1–H4 during the blank-

ing period. Setting HBLKMASK high will set H1 = H3 = low and

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