AT42QT1481_14 Datasheet, PDF (44/73 Pages) ATMEL Corporation – 48-Key QMatrix FMEA IEC/EN60730 Touch Sensor IC

5.11
Oscilloscope Sync – SSYNC
The S_Sync pin can output a positive pulse oscilloscope sync that brackets the burst of a selected X line. More than
one burst can output a sync pulse as determined by the Setups parameter SSYNC for each X line (see Table 5-3).
This feature is invaluable for diagnostics; without it, observing signals clearly on an oscilloscope for a particular burst
is very difficult.
The bits of this Setup byte are allocated as shown in Table 5-3.
Table 5-3. SSYNC Bits
Bit
Scope Sync Output When Burst On...
7
X7
6
X6
5
X5
4
X4
3
X3
2
X2
1
X1
0
X0
Note: STS_DEBUG shares the use of Pin 43 with SSYNC, but only one feature should be enabled at a time. To
prevent interference, all SSYNC bits should be set to zero (Off) if Debug output is desired.
This function is supported in Atmel QmBtn PC software.
SSYNC Default value:
0 (Off)
5.12
Negative Hysteresis – NHYST
The QT1481 employs programmable hysteresis levels of 6.25%, 12.5%, 25%, or 50%. The hysteresis is a
percentage of the distance from the threshold level back towards the reference, and defines the point at which a
touch detection drops out. A 12.5% hysteresis point is closer to the threshold level than to the signal reference level.
Hysteresis prevents chatter and works to make key detection more robust. Hysteresis is only used once the key has
been declared to be in detection, in order to determined when the key should drop out.
Excessive amounts of hysteresis can result in stuck keys that do not release. Conversely, low amounts of hysteresis
can cause key chatter due to noise or minor amounts of finger motion.
The hysteresis levels are set for all keys only; it is not possible to set the hysteresis differently from key to key.
NHYST Typical values:
0, 1 (6.25%, 12.5%)
NHYST Default value:
1 (12.5%)
NHYST Possible range:
0, 1, 2, 3 (6.25%, 12.5%, 25%, 50%)
AT42QT1481 [DATASHEET]
44
9621EX–AT42–07/2014