www.ti.com.......................................................................................................................................................... SBAS406B – JUNE 2008 – REVISED MARCH 2009
The control byte begins with a start bit followed by seven control bits. For the command to be valid, the start bit
must be '1'. Do not use '0' for the start bit; it is reserved for factory use.
Initiate Start—The first bit is the start bit (S), and must always be high to initiate the start of a user-controllable
control byte. When the start bit = '0', it is reserved for factory use.
Addressing and Command Decoding—The next three bits in the control byte following the start bit are three
addressing bits A[2:0] used to select the active input channel(s) of the input multiplexer (see
Table 4 and
Figure 24), enable the touch screen drivers, select the reference inputs, or decode other commands.
Bit[6:4] = '010' is the setup command that is used to configure the TSC.
Bit[3:0] followed by the setup command are the configuration bits and are used to select the pull-up resistor
value, bypass the noise filter (in the preprocessing unit), select the SDO output timing, and perform the software
reset. Bit[3:1] are static—that is, they do not change once programmed unless either the device is powered off,
one of the reset conditions occur (power-on reset, software reset, or SureSet), or unless changed with the setup
command. Note that if any reset occurs, bit[3:1] is set to the default values listed in
Table 3. Any function
decoded as shown in
Table 4 (excluding the setup command) has no access to these four configuration bits.
Table 4. Converter Function Select (CFS) Information
BIT 2(1)
INPUT TO
A[2:0]
SER/DFR
+REF
–REF = –IN
ADC = +IN
X-DRIVERS
Y-DRIVERS
DESCRIPTION
0h
Don't care
VDD
GND
TEMP1
All OFF
Measure TEMP1
1h
1 (single-ended)
VDD
GND
X+
All OFF
All ON
Measure Y position
1h
0 (differential mode)
Y+
Y–
X+
All OFF
All ON
Measure Y position
Used as noise filter
2h
—
All OFF
Setup command(2)
bypass
3h
1 (single-ended)
VDD
GND
X+
X– ON
Y+ ON
Measure Z1 position
3h
0 (differential mode)
Y+
X–
X+
X– ON
Y+ ON
Measure Z1 position
4h
1 (single-ended)
VDD
GND
Y–
X– ON
Y+ ON
Measure Z2 position
4h
0 (differential mode)
Y+
X–
Y–
X– ON
Y+ ON
Measure Z2 position
5h
1 (single-ended)
VDD
GND
Y+
All ON
All OFF
Measure X position
5h
0 (differential mode)
X+
X–
Y+
All ON
All OFF
Measure X position
6h
Don't care
VDD
GND
AUX
All OFF
Measure AUX
7h
Don't care
VDD
GND
TEMP2
All OFF
Measure TEMP2
(1)
Bit 2 is the SER/DFR control bit for all commands except for the setup command.
(2)
Use the setup command to configure the touch screen controller or access the software reset function.
MODE—The mode bit sets the resolution of the A/D converter. With this bit low, the next conversion has 12 bits
of resolution; with this bit high, the next conversion has eight bits of resolution.
SER/DFR—The SER/DFR bit controls the reference mode: either single-ended (high) or differential (low). The
differential mode is also referred to as the ratiometric conversion mode and is preferred for X-Position,
Y-Position, and Pressure-Touch measurements for optimum performance. The reference is derived from the
voltage at the switch drivers, which is almost the same as the voltage to the touch screen. In this case, a
reference voltage is not needed because the reference voltage to the A/D converter is the same as the voltage
across the touch screen. In single-ended mode, the converter reference voltage is always the difference between
If X-Position, Y-Position, and Pressure-Touch are measured in the single-ended mode, then VDD is used as the
reference.
NOTE: The differential mode can only be used for X-Position, Y-Position, and Pressure-Touch measurements.
All other measurements require the single-ended mode.
Copyright 2008–2009, Texas Instruments Incorporated
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