at42qt2100 ATMEL Corporation, at42qt2100 Datasheet - Page 11

• Manufacturer Part Number: at42qt2100
• Description: Qtouch Touch Sensor Ic
• Manufacturer: ATMEL Corporation

4. Detailed Operation
4.1
4.1.1
4.1.2
4.1.3
4.1.4
9554CX–AT42–11/11
Reset
Introduction
Delay to SPI Functionality
Reset Delay to Touch Detection
Mode Setting After Reset
When starting from power-up or RESET reset there are a few additional factors to be aware of.
In most applications the host will not need to take special action.
During hardware reset all outputs are disabled. To define the levels of the CHANGE and
DRDY during reset these signals should pulled down by resistors to 0V. Otherwise, they may
drift high causing the host to detect a false logic 1.
When the initial reset phase ends, CHANGE and DRDY outputs are enabled. DRDY will drive
low and CHANGE will drive high.
The QT2100 SPI interface is not operational while the device is being reset. However, SPI is
made operational early in the start-up procedure.
After any reset (either via the RESET pin or via power-up), SPI typically becomes operational
within 50 ms of RESET going high or power-up. CHANGE is pulled high, and held high until
the device status is read by the host micro-controller, to indicate completion of the initialization
sequence after power-on or reset.
After power-up or reset, the QT2100 calibrates all electrodes.
During this time, touch detection cannot be reported. Calibration completes after 15 burst
cycles, which takes approximately 350 ms, depending on the electrode layout and Cs
selection.
In total, 400 ms are required from reset or power-up for the device to be fully functional.
Disabled Keys: Keys with missing Cs capacitors, or that otherwise have an out-of-range
signal during calibration, are considered to be unused or faulty and are disabled. Disabled
keys are re-examined for operation after each reset or recalibration event.
After a reset the device will enter Free Run mode, with AKS disabled.
AT42QT2100
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