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AT42QT2100 Datasheet(PDF) 12 Page - ATMEL Corporation |
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AT42QT2100 Datasheet(HTML) 12 Page - ATMEL Corporation |
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12 / 44 page  12 AT42QT2100 [DATASHEET] 9554E–AT42–01/13 4. Detailed Operation 4.1 Reset 4.1.1 Introduction 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 0 V. 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. 4.1.2 Delay to SPI Functionality 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. 4.1.3 Reset Delay to Touch Detection 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. 4.1.4 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. 4.1.5 Mode Setting After Reset After a reset the device will enter Free Run mode, with AKS disabled. 4.2 Communications 4.2.1 Introduction The QT2100 communicates as a slave device over a full-duplex 4-wire (MISO, MOSI, SCK, SS) SPI interface. In addition there is a DRDY pin which indicates when the QT2100 is carrying out acquisition bursts and a CHANGE pin which is asserted when a change occurs in the status of the touch sensors (see Table 4-1). Table 4-1. Additional Pins Pin High Low DRDY Burst is complete Burst is active CHANGE New touch data Latest data has already been read by host |
Similar Part No. - AT42QT2100_14 |
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Similar Description - AT42QT2100_14 |
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