MXB7846(2004) 查看數據表（PDF） - Maxim Integrated

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MXB7846
(Rev.:2004)

2.375V to 5.25V, 4-Wire Touch-Screen Controller with Internal Reference and Temperature Sensor

Maxim Integrated 

2.375V to 5.25V, 4-Wire Touch-Screen Controller

with Internal Reference and Temperature Sensor

Data Format

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.

Applications Information

Basic Operation of the MXB7846

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 VDD and ground on an alternate

basis. For example, to measure the Y position when a

pointing device presses on the touch screen, the Y+

CS

1

DCLK

8

15 1

and Y- drivers are turned on, connecting one side of

the vertical resistive layer to VDD and the other side to

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

8

15 1

DIN

S

CONTROL BYTE 0

S

CONTROL BYTE 1

S CONTROL BYTE 2

DOUT

BUSY

B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0

CONVERSION RESULT 0

Figure 10. 15-Clock/Conversion Timing

B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0

CONVERSION RESULT 1

CS

1

8

DCLK

16

1

8

...

16

...

DIN S

CONTROL BYTE 0

DOUT

BUSY

S

CONTROL BYTE 1

B11 B10 B9 B8 B7 B6 B5 B4 B3 B2 B1 B0

CONVERSION RESULT 0

...

B11 B10 B9 B8 B7 B6 . . .

CONVERSION RESULT 1

...

Figure 11. 16-Clock/Conversion Timing

______________________________________________________________________________________ 17

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