C.3.1. Touchscreen interface architecture

Figure C.7 shows the touchscreen interface. Table C.3 lists the touchscreen control signals. The signals to the touchscreen are routed to connector J13.

Table C.3. Touchscreen host interface signal assignment

Signal nameDescription
TSMOSISerial data input to controller
TS_nSSChip select
TSSCLKClock input
TSMISOData output
TSnDAVData available
TSnPENIRQPen down interrupt
TSnKPADIRQKeypad interrupt
VBAT[2:1] and AUX[2:1]External voltage to analog to digital converter in touchscreen controller. These are reserved for expansion for external devices connected to the AD and keypad connector J13.
R[4:1] and C[4:1]Row and column scan signals for a keyboard. The expansion board switches S3 to S8 currently use eight positions on the scan matrix, but additional switches can be fitted using the AD and keypad connector J13.

Figure C.7. Touchscreen and keypad interface

Touchscreen and keypad interface

The connection between the resistive elements of the touchscreen and J3, J8, or J10 is shown in Figure C.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 C.8. Touchscreen resistive elements

Touchscreen resistive elements

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