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.
Note
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 name | HDRB connector | Description |
|---|
| TS_DIN | F2 | Serial data input to controller |
| TS_nCS | F1 | Controller chip select |
| TS_DCLK | F0 | Clock input to controller |
| TS_DOUT | F3 | Data output from controller |
| TS_BUSY | Not connected | Busy indicator from controller |
| TS_nPENIRQ | F4 | Interrupt from controller (drives the TSPENINT
bit of the PIC) |
Figure 4.7 shows
the pinout of the touchscreen connector J16.
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.
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