Control Byte
MODE—The mode bit sets the resolution of the ADC. With
this bit low, the next conversion has 12 bits of resolution,
whereas with this bit high, the next conversion has 8 bits of
resolution.
The control byte (on DIN), as shown in Table III, provides the
start conversion, addressing, ADC resolution, configuration,
and power-down of the TSC2046. Figure 9 and Tables III and
IV give detailed information regarding the order and descrip-
tion of these control bits within the control byte.
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 refer-
ence 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 as the reference
voltage to the ADC is the voltage across the touch screen. In
the single-ended mode, the converter reference voltage is
Bit 7
Bit 0
(LSB)
(MSB)
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
S
A2
A1
A0
MODE SER/DFR PD1
PD0
TABLE III. Order of the Control Bits in the Control Byte.
BIT
NAME
DESCRIPTION
7
S
Start bit. Control byte starts with first high bit on DIN.
A new control byte can start every 15th clock cycle
in 12-bit conversion mode or every 11th clock cycle
in 8-bit conversion mode (see Figure 13).
always the difference between the V
REF and GND pins (see
Tables I and II, and Figures 2 through 5 for further informa-
tion).
6-4
3
A2-A0
MODE
Channel Select bits. Along with the SER/DFR bit, these
bits control the setting of the multiplexer input, touch driver
switches, and reference inputs (see Tables I and II).
If X-Position, Y-Position, and Pressure-Touch are measured
in the single-ended mode, an external reference voltage is
needed. The TSC2046 must also be powered from the
external reference. Caution should be observed when using
the single-ended mode such that the input voltage to the
ADC does not exceed the internal reference voltage, espe-
cially if the supply voltage is greater than 2.7V.
12-Bit/8-Bit Conversion Select bit. This bit controls
the number of bits for the next conversion: 12-bits
(low) or 8-bits (high).
2
SER/DFR Single-Ended/Differential Reference Select bit. Along
with bits A2-A0, this bit controls the setting of the
multiplexer input, touch driver switches, and reference
inputs (see Tables I and II).
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.
1-0
PD1-PD0 Power-Down Mode Select bits. Refer to Table V for
details.
TABLE IV. Descriptions of the Control Bits within the Control Byte.
PD0 and PD1—Table V describes the power-down and the
internal reference voltage configurations. The internal refer-
ence voltage can be turned on or off independently of the
ADC. This can allow extra time for the internal reference
voltage to settle to the final value prior to making a conver-
sion. Make sure to also allow this extra wake-up time if the
internal reference is powered down. The ADC requires no
wake-up time and can be instantaneously used. Also note
Initiate START—The first bit, the S bit, must always be high
and initiates the start of the control byte. The TSC2046
ignores inputs on the DIN pin until the start bit is detected.
Addressing—The next three bits (A2, A1, and A0) select the
active input channel(s) of the input multiplexer (see Tables I, II,
and Figure 2), touch screen drivers, and the reference inputs.
CS
tACQ
DCLK
DIN
1
8
1
8
1
8
SER/
DFR
S
A2 A1 A0 MODE
Idle
PD1 PD0
Acquire
(START)
Conversion
Idle
BUSY
DOUT
11 10
(MSB)
9
8
7
6
5
4
3
2
1
0
Zero Filled...
(LSB)
Drivers 1 and 2(1)
(SER/DFR High)
Off
Off
On
Off
Drivers 1 and 2(1, 2)
(SER/DFR Low)
On
Off
NOTES: (1) For Y-Position, Driver 1 is on X+ is selected, and Driver 2 is off. For X-Position, Driver 1 is off, Y+ is selected,
and Driver 2 is on. Y– will turn on when power-down mode is entered and PD0 = 0. (2) Drivers will remain on if PD0 = 1 (no
power down) until selected input channel, reference mode, or power-down mode is changed, or CS is high.
FIGURE 9. Conversion Timing, 24 Clocks-per-Conversion, 8-Bit Bus Interface. No DCLK delay required with dedicated serial port.
TSC2046
SBAS265C
13
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