at42qt1481 ATMEL Corporation, at42qt1481 Datasheet - Page 43

• Manufacturer Part Number: at42qt1481
• Description: 48-key Qmatrix Ic
• Manufacturer: ATMEL Corporation

5.6
5.7
5.8
9621B–AT42–06/11
Detect Integrator Multiplier – DIM
Negative Recal Delay – NRD
Positive Recalibration Delay – PRD
It is sometimes useful to be able to operate the QT1481 with a higher detect integrator limit than
can be set with NDIL alone. The Detect Integrator Multiplier (DIM) is a multiplier which extends
the range of NDIL. The operating detect integrator limit for a key is arrived at by multiplying NDIL
for that key by DIM. Note that the detect integrator range is extended at the expense of the step
size.
This function is programmed on a global basis. See
Table 5-2.
If a key is disabled with NDIL = 0, DIM is ignored.
DIM Default value: 0 (x1)
DIM Possible range: 0, 1, 2, 3 (x1, x2, x4, x8)
If an object unintentionally contacts a key resulting in a detection for a prolonged interval it is
usually desirable to recalibrate the key in order to restore its function, perhaps after a time delay
of some seconds.
The Negative Recal Delay timer monitors such detections. If a detection event exceeds the
timer's setting, the key is automatically recalibrated. After a recalibration has taken place, the
affected key once again functions normally even if it is still being contacted by the foreign object.
This feature is set on a per-key basis using the NRD setup parameter.
NRD can be disabled by setting it to zero (infinite timeout) in which case the key never
autorecalibrates during a continuous detection (but the host could still command it).
NRD is set using one byte per key, which can range in value from 0 – 254. NRD above 0 is
expressed in 0.5s increments. Thus if NRD = 120, the timeout value is actually 60 seconds.
Note:
NRD Typical values:
NRD Default value:
NRD Range:
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 by recalibrated to a new lower reference level.
Table 5-2
DIM
0
1
2
3
255 is an illegal number to use.
Extended Detect Integrator Limit
shows the extended detect integrator range for each value of DIM.
Multiplier
x1
x2
x4
x8
20 to 60 (10s to 30s)
20 (10s)
0 – 254 (, 0.5s – 127s)
Table 5-7 on page
Extended Integrator Limit
57.
AT42QT1481
8 – 120
1 – 15
2 – 30
4 – 60
43