at42qt1040 ATMEL Corporation, at42qt1040 Datasheet - Page 10

• Manufacturer Part Number: at42qt1040
• Description: Qtouch? 4-key Sensor Ic
• Manufacturer: ATMEL Corporation

4.4
4.5
10
Calibration
Debug Mode
AT42QT1040
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.
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:
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.
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).
Byte
10
11
12
13
14
15
16
17
0
1
2
3
4
5
6
7
8
9
Serial Data Output
Purpose
Frame Number
Chip Version
Reference 0 Low Byte
Reference 0 High Byte
Reference 1 Low Byte
Reference 1 High Byte
Reference 2 Low Byte
Reference 2 High Byte
Reference 3 Low Byte
Reference 3 High Byte
Signal 0 Low Byte
Signal 0 High Byte
Signal 1 Low Byte
Signal 1 High Byte
Signal 2 Low Byte
Signal 2 High Byte
Signal 3 Low Byte
Signal 3 High Byte
Notes
Framing index number 0-255
Upper nibble: major revision
Lower nibble: minor revision
Unsigned 16-bit integer
Unsigned 16-bit integer
Unsigned 16-bit integer
Unsigned 16-bit integer
Unsigned 16-bit integer
Unsigned 16-bit integer
Unsigned 16-bit integer
Unsigned 16-bit integer
Table
4-3.
9524B–AT42–04/09