21

The focus point is important and could affect the SQUAL

value. Figure 32 shows another setup with various z-

heights. This graph clearly shows that the SQUAL value is

dependent on focus distance.

Note: The data is obtained by getting multiple readings

over different heights.

SQUAL

Address: 0x04

Access: Read

Reset Value: 0x00

Bit

7

6

5

4

3

2

1

0

Field

SQ

7

SQ

6

SQ

5

SQ

4

SQ

3

SQ

2

SQ

1

SQ

0

Data Type: Upper 8 bits of a 9-bit integer.

USAGE: SQUAL (Surface QUALity) is a measure of the number of features visible by the sensor in the current frame.

Number of Features = SQUAL Register Value x 2.

The maximum value is 255. Since small changes in the current frame can result in changes in SQUAL, variations in SQUAL

when looking at a surface are expected. The graph below shows 250 sequentially acquired SQUAL values, while a sensor

was moved slowly over white paper. SQUAL is nearly equal to zero when there is no surface below the sensor.

1.50

1.25

1.00

0.75

0.50

0.25

0

DELTA FROM NOMINAL FOCUS (mm)

Figure 32. Typical Mean SQUAL vs. z

(white paper).

-1.0

-0.6

-0.2

0.2

0.6

1.0

σ

σ

3

3

–

+

X

X

X