Rainbow-electronics AT42QT1040 Manual do Utilizador descarregar pdf (Página 10)

9524A–AT42–03/09

AT42QT1040

4.4 Calibration

Calibration is the process by which the sensor chip assesses the background capacitance on

each channel. During calibration, a number of samples are taken in quick succession to get a

baseline for the channel’s reference value.

Calibration takes place ~50 ms after power is applied to the device. Calibration also occurs if the

Max On-duration is exceeded or a positive re-calibration occurs.

4.5 Debug Mode

An added feature to this device is a debug option whereby internal parameters from the IC can

be clocked out and monitored externally.

Debug mode is entered by shorting the CS3 capacitor (SNSK3 and SNS3 pins) on power-up

and removing the short within 5 seconds.

Note: If the short is not removed within 5 seconds, debug mode is still entered, but with

Channel 3 unusable until a re-calibration occurs. Note that as Channel 3 will show up as

being in detect, a recalibration will occur after Max On-duration (~30 seconds).

Debug CLK pin (OUT0

) and Debug Data pin (OUT1) float while debug data is not being output

and are driven outputs once debug output starts (that is, not open drain).

The serial data is clocked out at a rate of ~200 kHz, MSB first, as in Table 4-3.

Table 4-3. Serial Data Output

Byte Purpose Notes

0 Frame Number Framing index number 0-255

1Chip Version

Upper nibble: major revision

Lower nibble: minor revision

2 Reference 0 Low Byte

Unsigned 16-bit integer

3 Reference 0 High Byte

4 Reference 1 Low Byte

Unsigned 16-bit integer

5 Reference 1 High Byte

6 Reference 2 Low Byte

Unsigned 16-bit integer

7 Reference 2 High Byte

8 Reference 3 Low Byte

Unsigned 16-bit integer

9 Reference 3 High Byte

10 Signal 0 Low Byte

Unsigned 16-bit integer

11 Signal 0 High Byte

12 Signal 1 Low Byte

Unsigned 16-bit integer

13 Signal 1 High Byte

14 Signal 2 Low Byte

Unsigned 16-bit integer

15 Signal 2 High Byte

16 Signal 3 Low Byte

Unsigned 16-bit integer

17 Signal 3 High Byte

1 2 ... 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Sensor IC 1
AT42QT1040 1

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