at42qt2100 ATMEL Corporation, at42qt2100 Datasheet - Page 13

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

4.2.3
9554CX–AT42–11/11
DRDY Pin
Similarly, when a custom threshold or LPM is sent to the QT2100, the CHANGE line is
asserted to indicate that the new setting has been applied and is shown in the “Normal
Exchange” data.
CHANGE also goes high after a reset to indicate to the host that it should do an SPI transfer in
order to provide initial configuration information to the QT2100 (as it does on every SPI
transfer).
CHANGE is driven low only once the data has been read through an SPI transfer.
In the case of a transient touch on one of the sensors, in which the touch has been removed
before the host has read the status of the sensors, the Change line remains asserted. Note
that in this case the data that will be read may be identical to the data that was previously
read.
The Data Ready (DRDY) pin is a quick indication of the QT2100 activity. During channel
acquisition bursts the pin is held low by the device, and driven high for ~500 µs in between
bursts. During processing and sleep the pin is driven high continuously, unless a 3-byte
communications exchange has taken place since the last acquisition burst.
After a 3-byte exchange has completed the pin is pulled low and remains low until the next
burst completion, after which the normal cycle resumes. This allows the host to detect if the
3-byte exchange packets have become de-synchronized.
The QT2100 has a DRDY grace period. If communications start during the 20 µs after DRDY
has been deasserted (pulled low) by the QT2100, then DRDY is reasserted and held high until
the exchange is complete. Key measurement bursts do not take place during this time.
AT42QT2100
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