AT42QT1111-MU_14 Datasheet, PDF (17/50 Pages) ATMEL Corporation – 11-key QTouch Touch Sensor IC

4.3 Sleep Mode
The QT1111 can be put into a very low power sleep mode (typically < 2 µA). During sleep mode, no keys are
measured and the DETECT outputs are all put into high impedance mode to minimize current consumption. The
device remains in sleep mode until a falling edge is detected on either the SS pin or the CHANGE pin. When the
QT1111 wakes from sleep mode, it continues to operate as it was before it was put into sleep mode. The QT1111
requires approximately 100 µs to wake from sleep mode and will not respond correctly to SPI communications until
the wake-up procedure is complete. The low level on the SS or CHANGE pin that is used to wake the device must be
maintained for 100 µs to ensure correct operation.
Note: If the device is set to sleep mode for an extended period, the host should initiate a recalibration immediately
after waking the QT1111.
4.4 Calibration
The device can be forced to recalibrate the sensor keys at any time. This can be useful where, for example, a
portable device is plugged into mains power, or during product development when settings are being tuned.
The QT1111 can also be configured to automatically recalibrate if it remains in detection for too long. This avoids
keys becoming “stuck” after a prolonged period of uninterrupted detection. See Section 7.17 on page 36 for details.
4.5 CHANGE Pin
The CHANGE pin can be configured using the Comms Options setup byte (see Section 7.5 on page 29) to act in one
of two modes:
 Data mode
 The CHANGE pin is asserted (pulled low) when the detection status of a key changes from that last
sent to the host; that is when a key-touch or key-release event occurs.
 The CHANGE pin is pulled low when a key status changes and is only released when the “Send All
keys” report is requested (0xC1), or the key status information bytes are read in Quick SPI mode (see
Section 7.5 on page 29).
 Touch mode
 The CHANGE pin is pulled low when one or more keys are in detect. The CHANGE pin remains low as
long as there is a key in detect, regardless of communications.
 The CHANGE pin is released when there are no keys in detect. No host communications are required
to release the CHANGE pin.
4.6 Stand-alone Mode
The QT1111 can operate in a stand-alone mode without the use of the SPI interface. The settings are loaded from
EEPROM and the device operates in 7-key mode using the Detect outputs.
4.7 Key Modes
4.7.1
11-key Mode
In 11-key mode, the device can sense up to 11 keys. Alternatively, one key can be replaced by the SYNC line as an
external trigger input (see Section 4.8.2 on page 18).
11-key mode is configured by setting the MODE bit in the Device Mode setup byte (see Section 7.4 on page 28).
Key acquisition can be triggered in one of two ways: using the internal clock to trigger acquisition either at a fixed
repetition period or in a continuous “free run” mode (see Section 4.8.1), or using the SYNC pin to provide an external
trigger (see Section 4.8.2 on page 18),
AT42QT1111-MU / AT42QT1111-AU [DATASHEET]
17
9571C–AT42–05/2013