© Quantum Research Group Ltd.
being checked be first fully recalibrated in order to allow the
Cz and DAC offset values to alter.
If a key is outside of a limit, either of bits 2 and 3 of command
'e' will be set for that key. The error will also appear as an
error in a bitfield reported with command 'E'.
There is no mechanism by which keys will automatically
recalibrate if the reference drifts past a guardband boundary.
Individual keys or groups of keys can be recalibrated with a
single command depending on the current command scope.
The time required to recalibrate many keys is not
multiplicative; the cal process for multiple keys runs in
parallel.
2.11 Boundary Error Reporting
See also commands ‘e’, page 23; ^N, page 27
Unlike guardband error reporting, boundary error reporting
only works within the active ADC signal window segment in
which the key's signal resides. Complex factoring of Cz and
Offset are not required for these tests, and the tests do not
require that the key be recalibrated to see the error condition.
Drift compensation can cause a key's reference level to move
near to the border of the ADC's 8-bit signal window; this may
make a key inoperable if the reference pegs near zero,
depriving the signal of the ability to move further negative
when a key is touched. Normally the reference level should
be reasonably centered within the ADC's current range, i.e. at
a level of about 128 decimal / 0x80 hex.
The truth logic for reference level drift error reporting is:
e/b2 = Reference > 191
e/b3 = Reference < 64
where e/b2 is command 'e' bit 2, and e/b3 is command 'e' bit
3. If either bit is set, the key should be recalibrated using
command 'b'. Note that guardbanding errors (Section 2.8)
also use these same bits for error reporting, but
guardbanding does not usually affect these bits until after a
recalibration.
Each Reference Boundary error will also appear as an error
in a bitfield reported from command 'E'.
There is no mechanism by which keys can be made to
automatically recalibrate if the reference drifts past a window
boundary.
2.9 Adjacent Key Suppression (AKS™)
See also command ^P, page 27
QT60xx5 devices incorporate adjacent key suppression
(‘AKS’ - patent pending) that can be selected on a per-key
basis. AKS permits the suppression of multiple key presses
based on relative signal strength. This feature assists in
solving the problem of surface moisture which can bridge a
key touch to an adjacent key, causing multiple key presses.
This feature is also useful for panels with tightly spaced keys,
where a fingertip might inadvertently activate an adjacent key.
AKS works for keys that are AKS-enabled anywhere in the
matrix and is not restricted to physically adjacent keys; the
device has no knowledge of which keys are actually
physically adjacent. When enabled for a key, adjacent key
suppression causes detections on that key to be suppressed
if any other AKS-enabled key in the panel has a more
negative signal deviation from its reference.
This feature does not account for varying key gains (burst
length) but ignores the actual negative detection threshold
setting for the key. If AKS-enabled keys in a panel have
different sizes, it may be necessary to reduce the gains of
larger keys relative to smaller ones to equalize the effects of
AKS. The signal threshold of the larger keys can be altered to
compensate for this without causing problems with key
suppression.
Adjacent key suppression works to augment the natural
moisture suppression of narrow gated transfer switches
(Section 3.13), creating a more robust sensing method.
2.12 Device Status & Reporting
See also commands ‘7’, page 22; ‘e’, page 23;
‘E’, page
23;
‘k’, page 23, ‘K’, page 24
The device can report on the general device status or specific
key states including touches and error conditions, depending
on the command used.
Usually it is most efficient to periodically request the general
device status using command ‘7’ first, as the response to this
command is a single byte which reports back on behalf of all
keys. ‘7’ indicates if there are any keys detecting, calibrating,
or in error.
If command ‘7’ reports a condition requiring further
investigation, the host device can then use commands ‘e’, ‘E’,
‘k’ or ‘K’ to provide further details of the event(s) in progress.
This hierarchical approach provides for a concise information
flow using minimal data transfers and low host software
overhead.
Bit 4 of command 7 reports if there is a discrepancy between
the eeprom and the Flash ROM backup of the eeprom in
case of data corruption; it is also set whenever a Setup
parameter has changed but was not yet been copied into
Flash. See Section 4.6. Resetting the device will force the
eeprom changes to be copied to Flash if legitimate, or it will
2.10 Full Recalibration
See also command ‘b’, page 28
The devices fully recalibrate on powerup, after a hard reset, a
soft reset or after a recalibrate ‘b’ command using an
algorithm that seeks out the optimal level of R2R offset and
Cz cancellation on a per-key basis. After powerup or a reset
the matrix is scanned key by key and appropriate calibrations
are set for each in accordance with user-defined setup
information. Since the circuit can tolerate a very wide signal
range, it is capable of adapting to a wide mix of key sizes and
shapes having widely varying Cx coupling capacitances.
If a false calibration occurs due to a key touch or foreign
object on the keys during powerup, the affected key will
recalibrate again when the object is removed depending on
the settings of Positive Threshold and Positive Recal Delay
(Sections 2.2 and 2.7).
Full recalibration is distinct from fast-recalibration, wherein
only the Reference level is quickly adjusted. Full recalibration
requires 26 burst cycles to complete whereas fast
recalibration requires only one cycle (Section 2.5). The time
required for recalibration is dependent on the burst spacing
setting ^G (Section 3.8).
lQ
8
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QT60xx5 / R1.05
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