Datasheet

11
AT42QT1040 [DATASHEET]
9524D–AT42–05/2013
4.5 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 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.
4.6 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 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
1 Chip 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