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AT42QT1085-MUR

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27P28-P30
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AT42QT1085 [DATASHEET]
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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 a reset all outputs are disabled. To define the levels of CHANGE
during reset this pin should pulled up to VDD
with a 10 k to 1M resistor.
When the initial reset phase ends the CHANGE
output is enabled. CHANGE drives low.
A software reset may be requested via the Command Processor T6 object.
4.1.2 Delay to SPI Functionality
The QT1085 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 low, and held low until the message server 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 QT1085 calibrates all electrodes.
During this time, touch detection cannot be reported. Calibration completes after 15 burst cycles, which takes
approximately 150 ms, with typical QTouchADC settings.
In total, 200 ms are required from reset or power-up for the device to be fully functional.
4.1.4 Mode Setting After Reset
After a reset the device loads configuration settings from nonvolatile memory, either previously stored or default
settings.
4.2 Calibration
Calibration is the process by which the sensor chip assesses the background capacitance on each channel.
Channels are only calibrated on power-up and when:
The channel is enabled (that is, activated).
OR
The channel is already enabled and one of the following applies:
The channel is held in detect for longer than the Touch Automatic Calibration setting (refer to the
AT42QT1085 Protocol Guide for more information on TCHAUTOCAL setting in the Touch Configuration
T16 object).
Note: This does not apply to a guard channel.
The signal delta on a channel is at least the anti-touch threshold (ATCHCALTHR) in the anti-touch
direction (refer to the AT42QT1085 Protocol Guide for more information on the ATCHCALTHR in the
PROCG_TOUCHCONFIG_T16 object (Touch Configuration T16 object).
The user issues a recalibrate command.
A status message is generated on the start and completion of a calibration.
Note that the device performs a global calibration; that is, all the channels are calibrated together for power-on or
user-requested calibration. Only the individual channel is calibrated for an ATCHCALTHR recalibration.
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AT42QT1085 [DATASHEET]
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4.3 Communications
4.3.1 Introduction
The QT1085 communicates as a slave device over a full-duplex 4-wire (MISO, MOSI, SCK, SS) SPI interface. In
addition there is a CHANGE
pin which is asserted when a message is waiting to be read:
Low = Message waiting
High = No Message waiting
See Section 7.3 on page 19 for details of the SPI Configuration and Timing Parameters.
Figure 7-1 and Figure 7-2 on page 20 show the basic timing for SPI operation. The host does the clocking and
controls the timing of the transfers from the QT1085.
After the host asserts SS
low, it should wait >22 µs in low-power mode before starting SCK; in Free run mode, a
delay of 2 µs is sufficient. The QT1085 reads the MOSI pin with each rising edge of SCK, and shifts data out on the
MISO pin on falling edges. The host should do the same to ensure proper operation.
SS
must be held low for the duration of a communications exchange (a Read or Write operation). To begin a new
communications exchange, SS
must be pulled high for at least 2 ms after a Read or 10 ms after a Write and then
pulled low. SS
should be held high when not communicating; if SS is low this is taken as an indication of impending
communications.
In this case, extra current is drawn, as the QT1085 does not enter its lowest power Sleep mode.
All timings not mentioned above should be as in Figure 7-2 on page 20.
4.3.2 CHANGE Pin
The QT1085 has an open-drain CHANGE pin which notifies the host when a message is waiting to be read.
CHANGE
is released after each message has been read through an SPI transfer. If further messages are pending,
the QT1085 loads the next one into the Message Handler and then reasserts (pulls low) the CHANGE
pin.
4.4 Signal Processing
4.4.1 Power-up Self-calibration
On power-up, or after reset, all channels are typically calibrated and operational within 200 ms.
4.4.2 Drift Compensation
This operates to correct the reference level of each key automatically over time; it suppresses false detections caused
by changes in temperature, humidity, dirt and other environmental effects.
The QT1085 drifts as configured in the Touch Configuration T16 object (refer to the AT42QT1085 Protocol Guide for
more information).
4.4.3 Detection Integrator Filter
The device features a touch detection integration mechanism. This acts to confirm a detection in a robust fashion. A
counter is incremented each time a touch has exceeded its threshold and has remained above the threshold for the
current acquisition. When this counter reaches a preset limit the sensor is finally declared to be touched. If, on any
acquisition, the signal is not seen to exceed the threshold level, the counter is cleared and the process has to start from
the beginning.
The detection integrator is configured using the touch object Key T13. Refer to the AT42QT1085 Protocol Guide for
more information.
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4.4.4 Adjacent Key Suppression (AKS) Technology
Adjacent Key Suppression (AKS) technology is a patented method used to detect which touch object is touched when
objects are located close together. A touch in a group of AKS objects is only indicated on the object with the strongest
touch delta. This is assumed to be the intended object. Once an object in an AKS group is in detect, there can be no
further detections within that group until the object is released.
AKS is configured using the Key T13 object (refer to the AT42QT1085 Protocol Guide for more information).
Note: If a touch is in detect and then AKS is enabled, that touch will not be forced out of detect. It will not go
out of detect until the touch is released. AKS will then operate normally.
4.5 Operating Modes
4.5.1 Introduction
The basic operating modes are: Active, Idle and Sleep.
Cycle time for Idle and Active is set by the Power Configuration T7 object, with special cases of 255 for free run and 0
for Sleep.
If a touch is detected, the device switches to free run mode and attempts to perform the detect integrator noise filter (DI)
function to completion; if the DI filter fails to confirm a detection the device goes back to Idle mode.
If a key is found to be in detection the part switches to Active mode. If the key is enabled for reporting, a message is
generated and CHANGE
is asserted (pulled low).
MISO in LP Mode:
During the sleep portion of LP mode, MISO floats.
Command During LP Mode:
Once set to Sleep (cycle time = 0), the device carries out no acquisitions until the cycle
time is changed to >0.
Note: The SS pin must be pulled high in order for the device to enter its lowest power sleep mode. If SS is
held low, the device enters a higher power Sleep mode to enable SPI communications.
4.5.2 Sleep Mode
Sleep mode offers the lowest possible current drain, in the low microamp region. In this mode no acquisitions are
performed.
In Sleep mode Output GPIOs are held in their final state before going to sleep:
With a 0% PWM the GPIO is Off during sleep
With a 100% PWM the GPIO is On during sleep.
If any other PWM is applied then the state is indeterminate (could be On or Off).
If a haptic effect is playing at the time when Sleep mode is entered, the effect is paused and resumed upon exiting
Sleep mode if the trigger condition remains true.
4.5.3 Supply Sequencing
Vdd and AVdd should be powered by a single supply. Make sure that any lines connected to the device are below or
equal to Vdd during power-up. For example, if RESET
is supplied from a different power domain to the QT1085 Vdd
pin, make sure that it is held low when Vdd is off. If this is not done, the RESET
signal could parasitically couple
power via the QT1085 RESET
pin into the Vdd supply.
4.6 Debugging
The QT1085 provides a mechanism for obtaining raw data for development and testing purposes by reading data
from the Debug Signals T4 object. Refer to the AT42QT1085 Protocol Guide for more information on this object.
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24P25-P27P28-P30

AT42QT1085-MUR

Mfr. #:
Buy AT42QT1085-MUR
Manufacturer:
Microchip Technology / Atmel
Description:
Capacitive Touch Sensors 8 Channel QTouch Haptic Sensor IC
Lifecycle:
New from this manufacturer.
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