3.3.5 0x8T - Set Touch Threshold
7
1
6
0
5
T
5
4
T
4
3
T
3
2
T
2
1
T
1
0
T
0
The response to this command is the Standard Response
byte, returned on the next SPI shift.
0x8T power-up default setting: 10
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 value 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.
3.4 SPI - What to Send
The host should execute the following commands after
powerup self-cal cycle has completed (assuming a 50ms SPI
repetition rate):
1. 0x01 - Basic calibration (optional as this is done
automatically on power-up)
2. 0x8T - Set touch threshold (optional)
3. An endlessly repeating mixture of:
a. 0x00 (Null) - all commands except:
b. 0x03 (Drift compensate) - replace every nth Null
command with 0x03 where typically, n = 10
c. 0x04 (Error status) - use after any detection just
after a calibration or power-up to see if there is a
calibration error.
Note: the Null can be replaced by an empty /SS pulse if there
is no need for fast updates.
lQ
9
QT411-ISSG R6.01/1005
QUANTUM [ QUANTUM RESEARCH GROUP ]
