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
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. 0x4P - Set prox threshold (optional)
3. 0x8T - Set touch threshold (optional)
4. An endlessly repeating mixture of:
a. 0x00 (Null) - all commands except:
b. 0x03 (Drift compensate) - replace every nth Null
command where typically, n = 6
c. If there is ever an error bit set, send a 0x01.
If the error occurs frequently, then perhaps the ratio of drift
compensation to Nulls should be increased.
Note: the Null can be replaced by an empty /SS pulse if there
is no need for fast updates.
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
PROX pin will go high if this threshold is crossed. The PROX
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 (see Section ) for this to work.
0x8T power-up default setting: 10
lQ
9
QT510 R6.04/0505
QUANTUM [ QUANTUM RESEARCH GROUP ]
