TMP92CF30
2009-06-12
92CF30-491
3.19.4 X/Y position measuring procedure
During the routine of pen-touch and INT4 interrupt generation, execute a pen position
measuring following the procedure below:
<X position coordinate measurement>
Make the SPX and SMX switches ON, and the SPY and SMY switches OFF.
With this setting, an analog-voltage that shows the X position will be input to the
PG3/MY/AN3 pin.
The X-position coordinate can be measured by converting this voltage to digital code
using the AD converter.
<Y position coordinate measurement>
Make the SPY and SMY-switches ON, and the SPX and SMX switches OFF.
With this setting, an analog voltage that shows the Y position will be input to the
PG2/MX/AN2 pin.
The Y position can be measured by converting this voltage to digital code using the
AD converter.
The above analog voltage which is input to AN3 and AN2 pins during the X and Y
position measurement above can be determined with the ratio between the ON resistance
value of the switch in the TMP92CF30 and the resistance value in the touch screen as
shown in Figure 3.19.5.
Therefore, even when touching an end area on the touch screen, the analog input voltage
will be neither 3.3V nor 0.0V.
Note that the rate of each resistance varies. Remember to take this into consideration
during designing. It is also recommended that an average taken from several AD
conversions performed if required be adopted as the final correct value.
Figure 3.19.5 Calculation analog voltage
AVCC=3.3V
SPY (SPX)
ON-resistor: Rpy (Rpx)
typ.10
Ω
SMY (SMX)
ON-resistor: Rmy (Rmx)
typ.10
Ω
Touch screen resistor : Rty (Rtx)
The resistance depends on
the touch screen.
R1
R2
Touch-point
AN2 (AN3)-pin
[Analog input voltage to theAN2 and AN3 pins: Formula to calculate E1]
E1 = ((R2+Rmy) / (Rpy+Rty+Rmy))
×
AVCC [V]
Ex.) Where AVCC=3.3V, Rpy=Rmy=10
Ω
, R1=400
Ω
and R2=100
Ω
E1 = ((100+10) / (10+400+100+10)
×
3.3
= 0.698V
Note1: An X-coordinate position can be calculated in the same way
though above formula is for Y-coordinate position.
Note2: Rty = R1+R2.
Содержание TLCS-900/H1 Series
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