ASX340AT datasheet(31/54 Pages) ONSEMI

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ASX340AT

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External Memory Speed Requirement

For a 2 KB block of overlay to be transferred within a

frame time to achieve maximum update rate, the SPI NVM

must operate at a certain minimum speed.

TABLE 25. TRANSFER TIME ESTIMATE

Value

Type

Description

33.3ms

4.5 MHz

1ms

OVERLAY ADJUSTMENT

To ensure a correct position of the overlay to compensate

for assembly deviation, the overlay can be adjusted with

assistance from the overlay statistics engine:

• The overlay statistics engine supports a windowed

8-bin luma histogram, either row-wise (vertical) or

column-wise (horizontal).

• The calibration statistics can be used to perform an

automatic successive-approximation search of a

cross-hair target within the scene.

• On the first frame, the firmware performs a coarse

horizontal search, followed by a coarse vertical search

in the second frame.

• In subsequent frames, the firmware reduces the

region-of-interest of the search to the histogram bins

containing the greatest accumulator values, thereby

refining the search.

• The resultant row and column location of the cross-hair

target can be used to assign a calibration value to offset

selected overlay graphic image positions within the

output image.

• The calibration statistics patch also supports a manual

mode, which allows the host to access the raw

accumulator values directly.

Figure 30. Overlay Calibration

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