AD9891 datasheet(18/58 Pages) AD

18 / 58 page

REV. A

–18–

AD9891/AD9895

Individual Vertical Sequences

To generate the individual vertical sequences or patterns shown

in Figure 18, five registers are required for each sequence.

Table VII summarizes these registers and their respective bit

lengths. The start polarity (VTPPOL) determines the starting

polarity of the vertical sequence and can be programmed high

or low. The first toggle position (VTPTOG1) and second

toggle position (VTPTOG2) are the pixel locations within the line

where the pulse transitions. A third toggle position

(VTPTOG3) is also available for sequences 0 through 7. All

toggle positions are 10-bit values, which limits the placement of

a pulse to within 1024 pixels of a line. A separate register,

VSTART, sets the start position of the sequence within the line

(see Individual Vertical Regions section). The Length

(VTPLEN) Register determines the number of pixels between

each of the pulse repetitions, if any repetitions have been

programmed. The number of repetitions (VTPREP) simply

determines the number of pulse repetitions desired within a

single line. Programming “1” for VTPREP gives a single

pulse, while setting to “0” will provide a fixed dc output based

on the start polarity value. There is a total of 12 individual

sequences that may be programmed.

When specifying the individual regions, each sequence may be

assigned to any of the V1–V4 outputs. For example, Figure 19

shows a typical 4-phase V-clock arrangement. Two different

sequences are needed to generate the different pulsewidths.

The use of individual start positions for V1–V4 allows the four

outputs to be generated from two sequences. Figure 20 shows a

slightly different V-clock arrangement in which V2, V3, and V4

are simply shifted and/or inverted versions of V1. Only one

individual sequence is needed because all signals have the same

pulsewidth. The invert sequence registers (VINV) are used for

V3 and V4 (see Table VII).

Note that for added flexibility, the VTPPOL Registers (Start

Polarity) may be used as an extra toggle position.

Table VII. Individual VTP Sequence Parameters

Length

Range

Description

VTPPOL

High/Low

Starting Polarity of Vertical Transfer Pulse for Each Sequence 0–11

VTPTOG1

10b

0–1023 Pixel Location

First Toggle Position within Line for Each Sequence 0–11

VTPTOG2

10b

0–1023 Pixel Location

Second Toggle Position within Line for Each Sequence 0–11

VTPTOG3

10b

0–1023 Pixel Location

Third Toggle Position within Line for Each Sequence 0–7

VTPLEN

10b

0–1023 Pixels

Length between Pulse Repetitions for Each Sequence 0–11

VTPREP

12b

0–4095 Pulses

Number of Pulse Repetitions for Each Sequence 0–11 (0 = DC Output)

V1–V4

PROGRAMMABLE SETTINGS FOR EACH SEQUENCE:

1: START POLARITY

2: 1ST TOGGLE POSITION

3: 2ND TOGGLE POSITION (THERE IS ALSO A 3RD TOGGLE POSITION AVAILABLE FOR SEQUENCES 0 TO 7)

4: LENGTH BETWEEN REPEATS

5: NUMBER OF REPEATS

START POSITION OF SEQUENCE IS INDIVIDUALLY PROGRAMMABLE FOR EACH V1–V4 OUTPUT

Figure 18. Individual Vertical Sequence Programmability

V1 USES SEQUENCE 0

V2 USES SEQUENCE 0,

WITH DIFFERENT START POSITION

V3 USES SEQUENCE 1

V4 USES SEQUENCE 1,

WITH DIFFERENT START POSITION

Figure 19. Example of Separate V1–V4 Signals Using Two Individual Sequences

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