4.4.1. Touchscreen interface architecture

Figure 4.6 shows the touchscreen interface. The signals to the touchscreen are routed to the 50-pin connector J13 and also to J16.

Figure 4.6. Touchscreen interface


The values of C152 to C155 might require changing to match the characteristics of individual touch screens. The values fitted are satisfactory for most screen types.

The touchscreen interface uses an Analog Devices ADS7843 controller to provide an interface between a 4-wire resistive touch screen and the TSCI. The interface signals are shown in Table 4.1.

Table 4.6. Touchscreen host interface signal assignment

Signal nameHDRB connector Description
TS_DINF2Serial data input to controller
TS_nCSF1Controller chip select
TS_DCLKF0Clock input to controller
TS_DOUTF3Data output from controller
TS_BUSYNot connectedBusy indicator from controller
TS_nPENIRQF4Interrupt from controller (drives the TSPENINT bit of the PIC)

Figure 4.7 shows the pinout of the touchscreen connector J16.

Figure 4.7. J16 pinout

The connection between J16 and the resistive elements of the touchscreen are shown in Figure 4.8. When the pen is down, the two resistive elements touch and form a four-resistor network. Measuring the voltages at the two dividers indicates the X and Y positions.

Figure 4.8. Touchscreen resistive elements

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