WM8945
Production Data
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
C¯¯S/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.
PD, May 2011, Rev 4.1
90
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
