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AT42QT1060-MMUR

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AT42QT1060 [DATASHEET]
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2.4.3 PWM Mask
A 1 in any bit position in this mask sets the corresponding pin to operate in PWM mode when its user output buffer is
active and configured as an output. A zero sets the pin in digital mode. The PWM value is set in the PWM register
that is writable via I
2
C communication.
2.4.4 Detection Mask
A 1 in any bit position in this mask sets the corresponding pin to be controlled by the status register. If the pin is
configured as an output, it is asserted automatically if there is a detection on the corresponding sensor channel. A
zero in any bit sets the pin to be controlled by the user output buffer, allowing the user to control the pins directly.
2.4.5 Active Level Mask
A 1 in any bit position in this mask sets the corresponding pin to be active high if configured as an output. A zero sets
the pin to be active low.
2.5 Acquisition/Low Power Modes (LP)
There are several different acquisition modes. These are controlled via the Low Power (LP) mode byte (see Section
5.12 on page 20) which can be written to via I
2
C communication.
LP mode controls the intervals between acquisition measurements. Longer intervals consume lower power but have
increased response time. During calibration and during the detect integrator (DI) period, the LP mode is temporarily
set to LP mode 1 for a faster response.
The QT1060 operation is based on a fixed cycle time of approximately 16 ms. The LP mode setting indicates how
many of these periods exist per measurement cycle. For example, if LP mode = 1, there is an acquisition every cycle
(16 ms). If LP mode = 3, there is an acquisition every 3 cycles (48 ms), and so on.
SLEEP mode (LP mode = 0) is available for minimum current drain. In this mode, the device is inactive, with the
device status being held as it was before going to sleep, and no measurements are carried out.
LP settings above mode 32 (512 ms) result in slower thermal drift compensation and should be avoided in
applications where fast thermal transients occur.
If LP mode = 255 the device operates in Free-run mode. In this mode the device will not enter LP mode between
measurements. The device continuously performs measurements one after another, resulting in the fastest
response time but the highest power consumption.
2.6 Adjacent Key Suppression (AKS) Technology
The device includes the Atmel-patented Adjacent Key Suppression technology, to allow the use of tightly spaced
keys on a keypad with no loss of selectability by the user.
There can be one AKS group, implemented so that only one key in the group may be reported as being touched at
any one time. A key with a higher delta signal dominates and pushes a key with a smaller delta out of detect. This
allows a user to slide a finger across multiple keys with only the dominant key reporting touch.
The keys which are members of the AKS group can be set via the AKS mask (see Section 5.15 on page 21). Keys
outside the group may be in detect simultaneously.
For maximum flexibility there is no automatic key recalibration timeout on key detection. The user should issue a
recalibration command if the key has been in detect for too long, for example for more than 30 seconds (see Figure
2.10).
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AT42QT1060 [DATASHEET]
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2.7 Change Line
The Change line (see CHG in Figure 1-1 on page 4) signals when there is a change in state in the Detection or Input
status bytes and is active low. It is cleared (allowed to float high) when the host reads the status bytes.
If the status bytes change back to their original state before the host has read the status bytes (for example, a touch
followed by a release), the CHG
line will be held low. In this case, a read to any memory location will clear the CHG
line.
The CHG
line is open-drain and should be connected via a 100k resistor to Vdd. It is necessary for minimum power
operation as it ensures that the QT1060 can sleep for as long as possible. Communications wake up the QT1060
from sleep causing a higher power consumption if the part is randomly polled.
The keys enabled by the key bit mask or a change in the Input port status cause a key change interrupt (see Table 5-
1 on page 16). Create a guard channel by removing that key from the key mask and including it in the AKS mask.
Touching the guard channel does not cause an interrupt. The key and AKS masks are set by using the mask
commands (see Table 5-1).
2.8 Types of Reset
2.8.1 External Reset
An external reset logic line can be used if desired, fed into the RST pin. However, under most conditions it is
acceptable to tie RST
to Vdd.
2.8.2 Soft Reset
The host can cause a device reset by writing a nonzero value to the reset byte. This soft reset triggers the internal
watchdog timer on a ~16 ms interval.
After ~16 ms the device resets and wakes again.
After a further 30 ms initialization period the device begins responding to its I
2
C slave address.
After another ~80 ms the device asserts the CHG line to indicate it is ready for touch sensing.
The device NACKs any attempts to communicate with it during the first 30 ms of its initialization period.
After CHG
goes low, the device calibrates the sensing channels. When complete, the CHG pin is set low once again.
2.9 Moisture Tolerance
The presence of water (condensation, sweat, spilt water, and so on) on a sensor can alter the signal values
measured and thereby affect the performance of any capacitive device. The moisture tolerance of QTouch devices
can be improved by designing the hardware and fine-tuning the firmware following the recommendations in the
application note Atmel AVR3002: Moisture Tolerant QTouch Design (www.atmel.com/Images/doc42017.pdf).
2.10 Calibration
The command byte can force a recalibration at any time by writing a nonzero value to the calibration byte. This can
be useful to clear out a stuck key condition after a prolonged period of uninterrupted detection.
When the device recalibrates, it also autosenses which keys are enabled by examining the burst length of each
electrode. If the burst length is either too short (if there is a missing or open Cs capacitor) or too long (a Cs capacitor
is shorted), the key is ignored until the next calibration.
The count of the number of currently enabled keys is found in the status response byte. This number can change
after a CAL command; for example, if a Cs capacitor is intermittent.
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AT42QT1060 [DATASHEET]
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2.11 Guard Channel
The device has a guard channel option, which allows any key, or combination of keys, to be configured as a guard
channel to help prevent false detection. Guard channel keys should be more sensitive than the other keys (physically
bigger or larger Cs), subject to burst length limitations (see Section 2.12.3).
With guard channel enabled, the designated key(s) is connected to a sensor pad which detects the presence of
touch and overrides any output from the other keys using the chip AKS feature. The guard channel option is enabled
by an I
2
C command.
To enable a guard channel the relevant key should be removed from the key mask (see Table 5-1 on page 16). In
addition, the guard channel needs to be included within the AKS mask with the other keys for the guard function to
operate. Note that a detection on the guard channel does not cause a change request.
With the guard channel not enabled, all the keys work normally.
Figure 2-1. Guard Channel Example
2.12 Signal Processing
2.12.1 Detect Threshold
The device detects a touch when the signal has crossed a threshold level and remained there for a specified number
of counts (see Section 5.11 on page 19). This can be altered on a key-by-key basis using the key threshold I
2
C
commands.
2.12.2 Detect Integrator
The device features a fast detection integrator counter (DI filter), which acts to filter out noise at the small expense of
slower response time. The DI filter requires a programmable number of consecutive samples confirmed in detection
before the key is declared to be touched. There is also a fast DI on the end of the detection (see Section 5.20 on
page 23). The fast DI will not be applied at the start of a detection if a detection on any other channel has already
been declared.
2.12.3 Burst Length Limitations
In a balanced system common signals are regarded as thermal shifts and are removed by the relative referencing
drifting, if enabled. This means that the burst lengths must be similar. This can be checked by reading the reference
values (Address 52 – 63) and making sure that they are similar. The absolute maximum difference is that the
maximum value of reference is less than three times the minimum value amongst all the channels. It is
recommended having the burst lengths (references) as close together as possible, through better routing and layout.
For example, if the keys have references of 250, 230, 220, 240, 200 and 210, this is acceptable. If the keys have
references of 250, 230, 220, 240, 200 and 710, the efficiency of the relative referencing drifting will be affected. The
last key’s (710) layout should be changed or relative referencing be disabled. The closer the references are in value,
the better the relative referencing drifting performs.
Guard channel
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AT42QT1060-MMUR

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Manufacturer:
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Description:
Capacitive Touch Sensors INTEGRATED-CIRCUIT
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