After the PRD interval has expired and the auto- recalibration
has taken place, the affected key will once again function
normally. PRD is fixed at 1 second for all keys, and cannot
be altered.
5.9 Oscilloscope Sync - SSYNC
Pin 11 (S_Sync) can output a positive pulse oscilloscope
sync that brackets the burst of a selected key. More than one
burst can output a sync pulse as determined by the Setups
parameter SSYNC for each key.
5.7 Burst Length - BL
The SSYNC function does not become effective until the part
has been reset, or the desired key(s) are recalibrated.
The signal gain for each key is controlled by circuit
parameters as well as the burst length.
This feature is invaluable for diagnostics; without it,
observing signals clearly on an oscilloscope for a particular
burst is very difficult.
The burst length is simply the number of times the
charge-transfer (‘QT’) process is performed on a given key.
Each QT process is simply the pulsing of an X line once, with
a corresponding Y line enabled to capture the resulting
charge passed through the key’s capacitance Cx.
This function is supported in Quantum’s QmBtn PC software.
SSYNC Default value:
0 (Off)
QT60xx8 devices use a fixed number of QT cycles which are
executed in burst mode. There can be up to 64 QT cycles in
a burst, in accordance with the list of permitted values shown
in Table 5.3.
5.10 Mains Sync - MSYNC
The MSync feature uses the SYNC pin.
External fields can cause interference leading to false
detections or sensitivity shifts. Most fields come from AC
power sources. RFI noise sources are heavily suppressed
by the low impedance nature of the QT circuitry itself.
Increasing burst length directly affects key sensitivity. This
occurs because the accumulation of charge in the charge
integrator is directly linked to the burst length. The burst
length of each key can be set individually, allowing for direct
digital control over the signal gains of each key individually.
Noise such as from 50Hz or 60Hz fields becomes a problem
if it is uncorrelated with acquisition signal sampling;
uncorrelated noise can cause aliasing effects in the key
signals. To suppress this problem the SYNC input allows
bursts to synchronize to the noise source.
Apparent touch sensitivity is also controlled by the Negative
Threshold level (NTHR). Burst length and NTHR interact;
normally burst lengths should be kept as short as possible to
limit RF emissions, but NTHR should be kept above 6 to
reduce false detections due to external noise. The detection
integrator mechanism also helps to prevent false detections.
The noise sync operating mode is set by parameter MSYNC
in Setups.
BL Typical values:
BL Default value:
BL possible values:
2, 3 (48, 64 pulses / burst)
2 (48 pulses / burst)
16, 32, 48, 64
The sync occurs only at the burst for the lowest numbered
enabled key in the matrix; the device waits for the sync
signal for up to 100ms after the end of a preceding full matrix
scan, then when a negative sync edge is received, the matrix
is scanned in its entirety again.
5.8 Adjacent Key Suppression - AKS
These 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.
The sync signal drive should be a buffered logic signal, but
never a raw AC signal from the mains; slow or erratic edges
on MSYNC can cause the device to sync on the wrong edge,
or both edges. The device should only sync to the falling
edge.
Since Noise sync is highly effective and inexpensive to
implement, it is strongly advised to take advantage of it
anywhere there is a possibility of encountering low frequency
(i.e. 50/60Hz) electric fields. Quantum’s QmBtn software can
show such noise effects on signals, and will hence assist in
determining the need to make use of this feature.
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.
If the sync feature is enabled but no sync signal exists, the
sensor will continue to operate but with a delay of 100ms
from the end of one scan to the start of the next, and hence
will have a slow response time. A failed Sync signal (one
exceeding a 100ms period) will cause an error flag (see
commands 0x05, 0x06).
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.
MSYNC Default value:
MSYNC Possible range:
0 (Off
)
0, 1 (Off, On)
5.11 Burst Spacing - BS
The interval of time from the start of one burst to the start of
the next is known as the burst spacing. This is an alterable
parameter which affects all keys. The burst spacing can be
viewed as a scheduled timeslot in which a burst occurs. This
approach results in an orderly and predictable sequencing of
key scanning with predictable response times.
Adjacent key suppression works to augment the natural
moisture suppression of narrow gated transfer switches
creating a more robust sensing method.
AKS Default value:
0 (Off)
lQ
20
QT60248-AS R4.02/0405
QUANTUM [ QUANTUM RESEARCH GROUP ]
