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AT42QT1111-MU Datasheet(PDF) 17 Page - ATMEL Corporation |
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AT42QT1111-MU Datasheet(HTML) 17 Page - ATMEL Corporation |
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17 / 50 page  17 9571A–AT42–02/10 AT42QT1111-MU/AT42QT1111-AU 4.1.6.4 Quick SPI Mode timing In Quick SPI mode, the minimum time between byte exchanges is reduced to 100 µS. If a pause in communications of 100 ms is detected during reading of the 7-byte report, the QT1111 resets the exchange, and on the next byte read it returns byte 0 of the report. 4.2 Reset The QT1111 can be reset using one of two methods: • Hardware reset: An external reset logic line can be used if desired, fed into the RESET pin. However, under most conditions it is acceptable to tie RESET to Vdd. • Software reset: A software reset can be forced using the “Reset” control command. For both methods, the device will follow the same initialization sequence. If there any saved settings in the EEPROM, these are loaded into RAM. Otherwise the default settings are applied. Note: The SPI interface becomes active after the QT1111 has completed its startup sequence, taking approximately 320 ms after power on/reset. 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 impedience 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 37 for details. 4.5 CHANGE Pin The CHANGE pin can be configured using the Comms Options setup byte (see Section 7.5 on page 30) 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’s 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 30). |
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