Datasheet

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
register writes are required when the camera operating mode is
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
register timing information for the five fields is loaded at startup.
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
Register Length (Bits) Range Description
HPATNUM 5 0 to 31 H-pattern groups Total number of H-pattern groups, starting at Address 0x800.
FIELDNUM 3 0 to 7 fields Total number of applied fields. Set to 1 for single-field operation.
FIELD_SEL1 5 0 to 31 field groups Selected first field.
FIELD_SEL2 5 0 to 31 field groups Selected second field.
FIELD_SEL3 5 0 to 31 field groups Selected third field.
FIELD_SEL4 5 0 to 31 field groups Selected fourth field.
FIELD_SEL5 5 0 to 31 field groups Selected fifth field.
FIELD_SEL6 5 0 to 31 field groups Selected sixth field.
FIELD_SEL7 5 0 to 31 field groups Selected seventh field.