AD9974BBCZ datasheet(26/52 Pages) AD

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AD9974

Rev. A | Page 26 of 52

MODE REGISTERS

The mode registers contain registers to select the final field timing

of the AD9974. Typically, all of the field and H-pattern group

information is programmed into the AD9974 at startup. During

operation, the mode registers allow the user to select any combi-

nation of field timing to meet the current requirements of the

system. The advantage of using the mode registers in conjunction

with preprogrammed timing is that they greatly reduce the system

programming requirements during camera operation. Only a few

changed, rather than having to write in all of the vertical timing

information with each camera mode change.

A basic still camera application can require five fields of hori-

zontal timing: one for draft mode operation, one for autofocusing,

and three for still image readout. With the AD9974, all of the

Then, during camera operation, the mode registers select

which field timing to activate, depending on how the camera

is being used.

The AD9974 supports up to seven field sequences selected from

up to 31 preprogrammed field groups using the FIELD_SEL

registers. When FIELDNUM is greater than 1, the AD9974 starts

with Field 1 and increments to each Field n at the start of each VD.

Figure 35 provides examples of mode configuration settings.

This example assumes to have four field groups, Field Group 0

to Field Group 3, stored in memory.

Table 15. Mode Registers

Length (Bits)

Range

Description

HPATNUM

0 to 31 H-pattern groups

Total number of H-pattern groups, starting at Address 0x800.

FIELDNUM

0 to 7 fields

Total number of applied fields. Set to 1 for single-field operation.

FIELD_SEL1

0 to 31 field groups

Selected first field.

FIELD_SEL2

0 to 31 field groups

Selected second field.

FIELD_SEL3

0 to 31 field groups

Selected third field.

FIELD_SEL4

0 to 31 field groups

Selected fourth field.

FIELD_SEL5

0 to 31 field groups

Selected fifth field.

FIELD_SEL6

0 to 31 field groups

Selected sixth field.

FIELD_SEL7

0 to 31 field groups

Selected seventh field.

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