WM8945ECSSLASHR datasheet(90/169 Pages) WOLFSON

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WM8945

Production Data

PD, May 2011, Rev 4.1

Figure 36 Pen-Down Touch Panel Detection

Touch pressure can only be determined indirectly, using the results of two separate measurements. A

constant current is applied through the plates, and the voltage on each plate is measured. The

difference between the two voltages is proportional to the resistance between the plates, which is a

measure of the pressure being applied to the panel.

The configuration is illustrated in Figure 37. In this example, a constant current flows from the Top

(YP) connection to the Left (XN) connection. The Right (XP) and Bottom (YN) points are measured in

turn, and the difference, VX – VY is equal to IP x RC, where IP is the current applied and RC is the

resistance between the plates. The smaller the measured resistance, the greater the pressure being

applied.

Figure 37 Z-axis (Pressure) Touch Panel Measurement

GENERAL PURPOSE INPUT/OUTPUT

The WM8945 provides four multi-function pins which can be configured to provide a number of

different functions. These are digital input/output pins on the DBVDD power domain. The GPIO pins

are:



GPIO1



¯¯ /GPIO2



CIFMODE/GPIO3



SDOUT/GPIO4

Note that only GPIO1 is a dedicated GPIO pin; the other pins are shared with Control Interface

functions. The pins available for GPIO function depend on the selected Control Interface mode, as

described in Table 61.

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