qt511 Quantum Research Group, qt511 Datasheet - Page 8

• Manufacturer Part Number: qt511
• Description: Qwheel? Touch Slider Ic
• Manufacturer: Quantum Research Group

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.
Example: The host causes a burst to occur by sending a
0x00 Null command every 50ms (20 per second). Every 10th
command the host sends is a 0x03 (drift) command.
The maximum drift compensation slew rate in the reference
level is -
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.
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.
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.
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 u nnecessarily
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.
The response to this command is the Standard Response
byte, returned on the next SPI shift.
3.3.4 0x04 - Error Status
This command is used to read the current status of the
QT511. In particular it is used to detect if there is a sensing
error caused by a calibration or power-on at a bad time, ie
when a finger is on the sensing wheel and thereafter
removed.
The reported bits are as follows:
lQ
TABLE 3-1 - Command Summary
0x00
0x01
0x03
0x04
0x8T
Hex
50ms x 10 x 10 = 5.0 seconds
7
0
Command
Error Status
Drift Comp
Threshold
Calibrate
Null
6
0
5
0
What it does
Shift out data; cause acquire burst (if /SS rises again)
Force recalibration of reference; causes 10 sequential bursts
Power up default value = calibrated
Drift compensation request; causes acquire burst. Max drift rate is 1 count per ten 0x03 commands.
On the following SPI shift, returns the error status of the part; causes acquire burst. See Section 3.3.4.
Set touch threshold; causes acquire burst. Bottom 6 bits (‘T’) are the touch threshold value. (10TT TTTT)
Power up default value = 10
4
0
3
0
2
1
1
0
0
0
8
All bits except Bit 1 can be safely ignored.
The status byte should be read the first time there is a
detection just after a power-on reset or after a 0x01
calibration. If Bit 1 = 1, there was a calibration error and the
device should be immediately calibrated again using the 0x01
command. After the second calibration it should be checked
yet again (and so on) until there is no error.
If there is no error according to the sequence of the above
paragraph, it is not required to read this byte again.
The error byte is returned on the following SPI shift.
3.3.5 0x8T - Set Touch Threshold
The lower 6 bits of this command (T5..T0) are used to set the
touch threshold level. Higher numbers are less sensitive (ie
the signal has to travel further to cross the threshold).
Operand ‘T’ can range from 0 to 63. Internally the number is
multiplied by 4 to achieve a wider range. 0 should never be
used.
This number is normally set to 10, more or less depending on
the desired sensitivity to touch and the panel thickness.
Touch detection uses a hysteresis equal to 12.5% of the
threshold setting.
Both the touch bit (bit 7) in the standard response and the
DETECT pin will go high if this threshold is crossed. The
DETECT pin can be used to indicate to the host that the
device has detected a finger, without the need for SPI polling.
However the /SS line must remain high constantly so that the
device continues to acquire continuously, or /SS has to be at
least pulsed regularly for this to work.
The response to this command is the Standard Response
byte, returned on the next SPI shift.
0x8T power-up default setting: 10
Bit 7 = 1 indicates touch;
Bit 6 = 1 indicates QWheel type (QT501 or QT511)
Bits 5, 4, 3, 2: unused (0)
Bit 1 = 1 if calibration error
Bit 0 reserved (reports 0 or 1)
7
1
= 0 indicates no touch
= 0 indicates Linear type (QT401 or QT411)
6
0
T
5
5
T
4
4
QT511-ISSG R6.01/1005
T
3
3
T
2
2
T
1
1
T
0
0