Datasheet

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THEORY OF OPERATION
TOUCH SCREEN MEASUREMENTS
Conversion Controlled by TSC2004 Initiated by TSC2004 (TSMode 1)
t
COORDINATE
+
OH1
f
OSC
)2 @
ǒ
t
PVS
)t
PRE
)t
SNS
)
OH
DLY1
f
OSC
Ǔ
)2 @
ǒ
N @
ǒ(
B)2
)
@
f
OSC
f
ADC
)OH
CONV
Ǔ
@
ǒ
1
f
OSC
Ǔ
)
ǒ
L
PPRO
f
OSC
Ǔ
Ǔ
(5)
TSC2004
SBAS408E – JUNE 2007 – REVISED MARCH 2008
As noted previously in the discussion of the A/D converter, several operating modes can be used that allow great
flexibility for the host processor. This section examines these different modes.
In TSMode 1, before a pen touch can be detected, the TSC2004 must be programmed with PSM = 1 and one of
two scan modes:
1. X-Y-Z Scan (converter function select bits C[3:0] = Control Byte 1 D[6:3] = 0000); or
2. X-Y Scan (converter function select bits C[3:0] = Control Byte 1 D[6:3] = 0001).
See Table 7 for more information on the converter function select bits.
When the touch panel is touched, and the internal pen-touch signal activates, the PINTDAV output is lowered if it
is programmed as PENIRQ. The TSC2004 then executes the preprogrammed scan function without a host
intervention.
At the same time, the TSC2004 starts up its internal clock. It then turns on the Y-drivers, and after a programmed
panel voltage stabilization time, powers up the A/D converter and converts the Y coordinate. If preprocessing is
selected, several conversions may take place. When data preprocessing is complete, the Y coordinate result is
stored in a temporary register.
If the screen is still touched at this time, the X-drivers are enabled, and the process repeats, but measures the X
coordinate instead, and stores the result in a temporary register.
If only X and Y coordinates are to be measured, then the conversion process is complete. A set of X and Y
coordinates are stored in the X and Y registers. Figure 39 shows a flowchart for this process. The time it takes to
go through this process depends upon the selected resolution, internal conversion clock rate, panel voltage
stabilization time, precharge and sense times, and whether preprocessing is selected. The time needed to get a
complete X and Y coordinate (sample set) reading can be calculated by:
Where:
t
COORDINATE
= time to complete X/Y coordinate reading.
t
PVS
= panel voltage stabilization time, as given in Table 16 .
t
PRE
= precharge time, as given in Table 17 .
t
SNS
= sense time, as given in Table 18 .
N = number of measurements for MAV filter input, as given in Table 3 as N.
(For no MAV: M1-0[1:0] = '00', W1-0[1:0] = '00', N = 1.)
B = number of bits of resolution.
f
OSC
= TSC onboard OSC clock frequency. See Electrical Characteristics for supply frequency (SNSVDD).
f
ADC
= A/D converter clock frequency, as given in Table 15 .
OH1 = overhead time #1 = 2.5 internal clock cycles.
OH
DLY1
= total overhead time for t
PVS
, t
PRE
, and t
SNS
= 10 internal clock cycles.
OH
CONV
= total overhead time for A/D conversion = 3 internal clock cycles.
L
PPRO
= preprocessor preprocessing time as given in Table 31 .
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