The actual rate of change of the reference level depends on
whether there is an offset in the signal with respect to the
reference level, and whether this offset is continuous or not.
3.3.1 0x00 - Null Command
7
0
6
0
5
0
4
0
3
0
2
0
1
0
0
0
It is possible to modulate the drift compensation rate
dynamically depending on circumstances, for example a
significant rate of change in temperature, by varying the mix
of Drift and Null commands.
If the Drift command is issued while the device is in touch
detection (ie bit 7 of the Standard Response byte =1), the drift
function is ignored.
The Null command will trigger a new acquisition (if /SS rises),
otherwise, it does nothing. The response to this command is
the Standard Response byte.
This command is predominant once the device has been
calibrated and is running normally.
3.3.2 0x01 - Calibrate
7
0
6
0
5
0
4
0
3
0
2
0
1
0
0
1
Drift compensation during Free-Run mode is fixed at 6, which
results in a maximum rate of drift compensation rate of about
3secs / count; see Section 1.2.
This command takes ~525ms @ 3.3V to complete.
The drift compensation rate should be made slow, so that it
does not interfere with finger detection. A drift compensation
rate of 3s ~ 5s is suitable for almost all applications. If the
setting is too fast, the device can become unnecessarily
desensitized when a hand lingers near the element. Most
environmental drift rates are of the order of 10's or 100's of
seconds per count.
0x01 causes the sensor to do a basic recalibration. After the
command is given the device will execute 10 acquisition
bursts in a row in order to perform the recalibration, without
the need for /SS to trigger each of the bursts. The host should
wait for DRDY to rise again after the calibration has
completed before shifting commands again.
This command should be given if there is an error flag (bit 1
of the response byte when no touch detection in progress).
On power-up the device calibrates itself automatically and so
a 0x01 command is not required on startup.
3.3.4 0x4P - Set Proximity Threshold
7
0
6
1
5
P5
4
P4
3
P3
2
P2
1
0
P1
P0
This command is optional, but if it is not given, the proximity
detection function will work at a default setting of 10.
The response to this command is the Standard Response
byte. During calibration, device communications are
suspended.
The lower 6 bits of this command (P5..P0) are used to set the
proximity threshold level. Higher numbers are less sensitive
(ie the signal has to travel further to cross the threshold).
Operand ‘P’ can range in value from 0 to 63. Zero (0) should
never be used. Very low settings can cause excessive flicker
in the proximity result due to low level noise and drift.
3.3.3 0x03 - Drift Compensate
7
0
6
0
5
0
4
0
3
0
2
0
1
1
0
1
0x03 causes the sensor to perform incremental drift
compensation. This command must be given periodically in
order to allow the sensor to compensate for drift. The more
0x03 commands issued as a percentage of all commands,
the faster the drift compensation will be.
The 0x03 command must be given 10 times in order for the
device to do one count of drift compensation in either
direction. The 0x03 command should be used in substitution
of the Null command periodically.
P is normally in the range from 6 to 10. The prox threshold
has no hysteresis and should only be used for non-critical
applications where occasional detection bounce is not a
problem, like power activation (i.e. to turn on an appliance or
a display).
The prox bit in the standard response and the PROX pin will
both go high if the signal exceeds this threshold.
0x4P power-up default setting: 10
Example: The host causes a burst to occur by sending a
0x00 Null command every 50ms (20 per second). Every 6th
command the host sends is a 0x03 (drift) command.
The maximum drift compensation slew rate in the reference
level is -
50ms x 6 x 10 = 3.0 seconds
TABLE 3-1 - Command Summary
Hex
0x00
Command
What it does
Shift out data; cause acquire burst (if /SS rises again)
Null
Force recalibration of reference; causes 10 sequential bursts
0x01
0x03
0x4P
Calibrate
Drift Comp
Prox Thresh
Power up default value = calibrated
Drift compensation request; causes acquire burst. Max drift rate is 1 count per ten 0x03’s.
Set prox threshold; causes acquire burst. Bottom 6 bits (‘P’) are the prox threshold value. (01PP PPPP)
Power up default value = 10
Set touch threshold; causes acquire burst. Bottom 6 bits (‘T’) are the touch threshold value. (10TT TTTT)
Power up default value = 10
0x8T
Touch Thresh
lQ
8
QT510 R6.04/0505
QUANTUM [ QUANTUM RESEARCH GROUP ]
