AD9920ABBCZ datasheet(44/112 Pages) AD

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AD9920A

Rev. B | Page 44 of 112

Sequence Line Alternation

To support the timing requirements of some advanced CCDs

in a memory-efficient manner, the AD9920A can automatically

increment the sequence number at the end of a given line through

the use of the SEQ_ALT_INC register (V-Sequence Register 0x09,

Bit 20). It can also reset the sequence number to the sequence

defined in the field register through the SEQ_ALT_RST register

(V-Sequence Register 0x09, Bit 21). Combining these two registers

allows the user to create a loop of sequences for a given region.

See Figure 56 for an example of how to use these two functions

together. The example in Figure 56 uses the register settings

listed in Table 18.

With these settings, at Sequence Change Position 0 (SCP0),

the AD9920A steps into Sequence 2. Because the Sequence 2

SEQ_ALT_INC = 1 and the SEQ_ALT_RST = 0, at the end of

that line the sequence number automatically increments to

Sequence 3. In the same way, at the end of that line, the

sequence number automatically increments to Sequence 4.

Because SEQ_ALT_INC = 0 and SEQ_ALT_RST = 1 for

Sequence 4, the AD9920A automatically resets the sequence

number to the sequence defined for that region in the field register,

which in this case is Sequence 2. The AD9920A continues to loop

in this fashion between Sequence 2, Sequence 3, and Sequence 4

until it reaches the next sequence change position.

It is important to note that the sequence number can increment

only at the end of a line and cannot be used to create more complex

patterns within one line. This is distinctly different from the special

vertical sequence alternation mode, which allows the user to

concatenate multiple sequences within one line (see the Special

Vertical Sequence Alternation (SVSA) Mode section).

Table 18. Register Settings for the Example in Figure 56

Field Registers

Sequence 2 Registers

Sequence 3 Registers

Sequence 4 Registers

Sequence 6 Registers

SCP0 = 0, SEQ0 = 2

SEQ_ALT_INC = 1

SEQ_ALT_INC = 0

SCP1 = 6, SEQ1 = 6

SEQ_ALT_RST = 0

SEQ_ALT_RST = 1

SEQ_ALT_RST = 0

SCP1

ACTIVE

SEQUENCE #

234

SCP0

Figure 56. Example Output Using SEQ_ALT_INC and SEQ_ALT_RST Functions

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