qt401 Quantum Research Group, qt401 Datasheet - Page 8

• Manufacturer Part Number: qt401
• Description: Qslide? Touch Slider Ic
• Manufacturer: Quantum Research Group

adjusting the percentage of time that the device spends in
sleep.
The delay between the rising edge of /SS and the following
burst is <1ms to allow Vdd to stabilize. If the maximum spec
on /SS low (1s) is exceeded, the device will eventually come
out of sleep and calibrate again on its own. The 1s is a
minimum design guide, not a precise number; the actual time
can vary considerably from device to device and should not
be relied upon.
The DETECT, PROX, and DRDY lines will float for ~400µs
after wake from Sleep mode; see Section 1.3 for details.
After each acquisition burst, DRDY will rise again to indicate
that the host can do another SPI transmission.
3.3 Commands
Commands are summarized in Table 3-1. Commands can be
overlapped, i.e. a new command can be used to shift out the
results from a prior command.
All commands cause a new acquisition burst to occur when
/SS is raised again after the command byte is fully clocked.
Standard Response: All SPI shifts return a ‘standard
response’ byte which depends on the touch detection state:
No touch detection:
Is touch detection:
Note that touch detection calculated position is based on the
results of the prior burst, which is triggered by the prior /SS
rising edge (usually, from the prior command, or, from a
dummy /SS trigger - see Section 3.2.1).
There are 6 commands as follows.
3.3.1 0x00 - Null Command
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.
lQ
TABLE 3-1 - Command Summary
0x4P
0x8T
Hex
0x00
0x01
0x02
0x03
Touch Thresh
7
0
End Calibrate
Command
Prox Thresh
Drift Comp
Calibrate
Null
6
0
5
0
Bit 7 = 0 (0= not touched)
Bits 6, 5, 4, 3, 2: unused
Bit 1 = 1 if signal polarity error
Bit 0 = 1 if prox detection only
Bit 7 = 1 (1= is touched)
Bits 0..6: Contain calculated position
What it does
Shift out data; cause acquire burst (if /SS rises again)
Force recalibration of reference using fixed slider ends; cause 10 sequential bursts
Power up default value = calibrated
Auto-find slider end points; cause 20 sequential bursts.
Power up default value = disabled
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
4
0
3
0
2
0
1
0
0
0
8
3.3.2 0x01 - Calibrate
This command takes ~525ms to complete with the circuit
shown in Figure 1-1. This time can be reduced by using
smaller Cs capacitors. Smaller Cs capacitors may result in
loss of resolution unless the panel thickness is also reduced.
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 is present ).
Note that this command cancels the 0x02 ‘End Calibrate’
command if 0x02 was previously issued to the part; if end
calibration is desired, the 0x02 command must be reissued
again after the 0x01 command.
On power-up the device calibrates itself automatically and so
a 0x01 command is not required on startup.
The response to this command is the Standard Response
byte.
3.3.3 0x02 - End Calibrate
The command takes ~500ms to complete.
The 0x02 command should preferably only be performed
after the basic calibration (0x01) is done. If it is done at
another time, the end calibration may be inaccurate.
0x02 causes the sensor to relocate the reported endpoints of
the slider to automatically correspond to the physical ends,
using a special calibration process. After the command is
given the device will execute 20 acquisition bursts in a row in
order to perform the calibration, without the need for /SS
cycles to trigger each of the bursts.
The host should remain quiet during this period and obey
DRDY which will remain low until the process is done before
shifting the next command.
This command is optional, however if it is not used, two Rs
resistors should be used to set the end zones of the slider
(See Section 2.3).
Executing a calibrate command (0x01) cancels the End
Calibrate mode, and therefore the End Calibrate command
has to be performed again if desired. However, once the
0x01 / 0x02 command sequence is performed, it should
0
7
0
0
6
0
0
5
0
0
4
0
0
3
0
QT401 R10.04/0505
0
2
0
0
1
1
1
0
0