XPT2046

Touch Screen Controller

XP

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TOUCH

X-POSITION

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X-POSITION

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TOUCH

Z2-POSITION

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Figure 11. Pressure Measurement Block Diagrams

Digital Interface

See Figure 12 for the typical operation of the XPT2046 digital interface. This diagram assumes that the source of

the digital signals is a microcontroller or digital signal processor with a basic serial interface.Each communication

between the processor and the converter,such as SPI, SSI, or Microwire_ synchronous serial interface, consists of

eight clock cycles. One complete conversion can be accomplished with three serial communications for a total of

24 clock cycles on the DCLK input.

The first eight clock cycles are used to provide the control byte via the DIN pin. When the converter has enough

information about the following conversion to set the input multiplexer and reference inputs appropriately, the

converter enters the acquisition (sample) mode and, if needed, the touch panel drivers are turned on. After three

more clock cycles, the control byte is complete and the converter enters the conversion mode. At this point, the

input sample-and-hold goes into the hold mode and the touch panel drivers turn off (in single-ended mode). The

next 12 clock cycles accomplish the actual analogto-digital conversion. If the conversion is ratiometric(SER/DFR

= 0), the drivers are on during the conversion and a 13th clock cycle is needed for the last bit of the conversionr

esult. Three more clock cycles are needed to complete the last byte (DOUT will be low), which are ignored by the

converter.

Control Byte

The control byte (on DIN), as shown in Table 3, provides the start conversion, addressing, ADC resolution,

configuration,and power-down of the XPT2046. Figure 12, Table 3 and Table 4 give detailed information regarding

the order and description of these control bits within the control byte.

Initiate START—The first bit, the S bit, must always be high and initiates the start of the control byte. The

XPT2046 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

Table 1, Table 2, and Figure 5), touch screen drivers, and the reference inputs.

MODE—The mode bit sets the resolution of the ADC. With this bit low, the next conversion has 12 bits ofr

esolution,whereas with this bit high, the next conversion has eight bits of resolution.

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