Datasheet

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SBAS191F
FIGURE 8. X- and Y-Coordinate Touch Screen Scan, Initiated by Touch.
The time needed to get a complete X/Y-coordinate reading
can be calculated by:
(3)
t 2.5 s + 2 t + t + t 2N N
1
f
s
COORDINATE PVS
PRE
SNS AVG BITS
CONV
=
( )
+•+µ






µ 44.
where,
t
COORDINATE
= Time to Complete X/Y-Coordinate Reading
t
PVS
= Panel Voltage Stabilization time (see Table XII)
t
PRE
= Precharge time (see Table XXII)
t
SNS
= Sense time (see Table XXIII)
N
AVG
= Number of Averages (see Table X); for no averag-
ing, N
AVG
= 1
N
BITS
= Number of Bits of Resolution (see Table IX)
f
CONV
= A/D Converter Clock Frequency (see Table XI)
If the pressure of the touch is also to be measured, the
process will continue in the same way, but measuring the Z
1
and Z
2
values, and placing them in the Z
1
and Z
2
registers
(see Figure 9). As before, this process time depends upon
the settings described above. The time for a complete X, Y,
Z
1
, and Z
2
coordinate reading is given by:
(4)
t4.75s+3t+t+t4NN
1
f
s
COORDINATE PVS
PRE
SNS AVG BITS
CONV
=µ
( )
+•+µ






44.
Screen
Touch
Issue Interrupt
PENIRQ
Go to Host-Controlled
Conversion
Touch Screen Scan
X and Y
PENIRQ Initiated
Done
Done
No
No
Yes
Yes
Yes
No
No
Yes
Is Data
Averaging Done
Is Screen
Touched
Is Panel Voltage
Stabilization Done
Turn On Drivers: Y+, Y–
Start Clock
Store X-Coordinates in
X-Register
Power Down A/D Converter
Power Up A/D Converter
Reset PENIRQ and
Scan Trigger
Turn Off Clock
Convert X-Coordinates
Is PSM = 1
No
Yes
No
Is Screen
Touched
Is Data
Averaging Done
No
Yes
Yes
Is Panel Voltage
Stabilization Done
Convert Y-Coordinates
Turn On Drivers: X+, X–
Power Up A/D Converter
Store Y-Coordinates in
Y-Register
Reset PENIRQ and
Scan Trigger
Power Down A/D Converter
Turn Off Clock
Issue Data Available