AT42QT2640_14 Datasheet, PDF (49/73 Pages) ATMEL Corporation – 64-key 8-slider/wheel QMatrix FMEA

5.13 Address 1223 – Oscilloscope Sync – SSYNC
Table 5-14. SSYNC, Generate scope sync for burst on selected X lines.
Address
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
1223
X7
X6
X5
X4
X3
X2
Bit 1
X1
Bit 0
X0
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 which is divided into eight
separate bits, each allowing selection of a scope sync at the burst on one X line.
This feature is invaluable for diagnostics; without it, observing signals clearly on an oscilloscope for a particular burst
is very difficult.
Note: The oscilloscope sync and the debug clock output share an I/O pin, and will interfere with each other if both
are enabled at the same time. Ensure SSYNC and DEBUG are not enabled simultaneously.
This function is supported in Atmel’s QmBtn PC software.
SSYNC Default value:
0 (No scope sync for any burst)
SSYNC Range:
0 - 255 (No sync at any burst - sync at every burst)
5.14 Address 1224 – Frequency Hopping Mode / Positive Recalibration Delay
Table 5-15. Frequency Hopping Mode / Positive Recalibration Delay
Address
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
1224
FHM
Reserved
PRD
Bit 0
5.14.1 Frequency Hopping Mode – FHM
If frequency hopping is enabled, the QT2640 continually monitors the noise across all keys and switches frequency
to try and find the frequency with least signal noise. If frequency hopping is disabled, the QT2640 always uses the
same frequency, defined by FREQ0.
This function is programmed on a global basis. See Table 5-24 on page 56.
FHM Default value:
3 (Sweep)
FHM Range:
0 – 3 (0 = off
1 = Calibrate all keys after hop
2 = Adjust each key's reference during hop)
3 = Sweep)
5.14.2 Positive Recalibration Delay – PRD
A recalibration can occur automatically if the signal swings more positive than the positive threshold level. This
condition can occur if there is positive drift but insufficient positive drift compensation, or, if the reference moved
negative due to a NRD autorecalibration, and thereafter the signal rapidly returned to normal (positive excursion).
As an example of the latter, if a foreign object or a finger contacts a key for period longer than the Negative Recal
Delay (NRD), the key is recalibrated to a new lower reference level. Then, when the condition causing the negative
swing ceases to exist (the object is removed) the signal can suddenly swing back positive to near its normal
reference.
AT42QT2640 [PRELIMINARY DATASHEET]
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9684DX–AT42–12/13