mxb7846 Maxim Integrated Products, Inc., mxb7846 Datasheet - Page 17

• Manufacturer Part Number: mxb7846
• Description: Mxb7846 2.375v To 5.25v, 4-wire Touch-screen Controller With Internal Reference And Temperature Sensor
• Manufacturer: Maxim Integrated Products, Inc.

Figure 10. 15-Clock/Conversion Timing
Figure 11. 16-Clock/Conversion Timing
with Internal Reference and Temperature Sensor
The MXB7846 output data is in straight binary format as
shown in Figure 12. This figure shows the ideal output
code for the given input voltage and does not include
the effects of offset, gain, or noise.
The 4-wire touch-screen controller works by creating a
voltage gradient across the vertical or horizontal resis-
tive network connected to the MXB7846, as shown in
the Typical Application Circuit. The touch screen is
biased through internal MOSFET switches that connect
each resistive layer to V
basis. For example, to measure the Y position when a
pointing device presses on the touch screen, the Y+
2.375V to 5.25V, 4-Wire Touch-Screen Controller
DCLK
DOUT
BUSY
DOUT
DCLK
BUSY
DIN
DIN
CS
CS
S
1
S
1
Basic Operation of the MXB7846
Applications Information
CONTROL BYTE 0
______________________________________________________________________________________
CONTROL BYTE 0
DD
and ground on an alternate
8
8
B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
Data Format
B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
CONVERSION RESULT 0
15
CONVERSION RESULT 0
S
1
16
CONTROL BYTE 1
and Y- drivers are turned on, connecting one side of
the vertical resistive layer to V
ground. In this case, the horizontal resistive layer func-
tions as a sense line. One side of this resistive layer
gets connected to the X+ input, while the other side is
left open or floating. The point where the touch screen
is pressed brings the two resistive layers in contact and
forms a voltage-divider at that point. The data converter
senses the voltage at the point of contact through the
X+ input and digitizes it. The horizontal layer resistance
does not introduce any error in the conversion because
no DC current is drawn.
The conversion process of the analog input voltage to
digital output is controlled through the serial interface
between the A/D converter and the µP. The processor
controls the MXB7846 configuration through a control
byte (see Tables 3 and 4). Once the processor instructs
S
1
CONTROL BYTE 1
8
B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0
8
CONVERSION RESULT 1
15
B 1 1 B 1 0 B 9 B 8 B 7 B 6
DD
S
1
CONVERSION RESULT 1
and the other side to
CONTROL BYTE 2
16
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