WM8948ECSSLASHR datasheet(97/189 Pages) WOLFSON

97 / 189 page

Production Data

WM8948

PD, May 2011, Rev 4.1

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 38. 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.

WM8948

GND

LDOVDD

AUX

ADC

Pressure

Figure 38 Z-axis (Pressure) Touch Panel Measurement

GENERAL PURPOSE INPUT/OUTPUT

The WM8948 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 62.

CONTROL INTERFACE MODE

GPIO PIN AVAILABILITY

2-wire (I2C)

GPIO1

GPIO2

GPIO3

GPIO4

3-wire (SPI)

GPIO1

GPIO3

GPIO4

4-wire (SPI)

GPIO1

GPIO3

Table 62 GPIO Pin Availability

Note that CIFMODE/GPIO3 pin selects between I2C and SPI Control Interface modes (see “Control

Interface”). To enable GPIO functions on GPIO3, the MODE_GPIO register bit must be set in order

to disconnect this pin from the Control Interface circuit. Setting the MODE_GPIO register bit causes

the Control Interface mode selection to be latched; it will remain latched until a Software Reset or

Power On Reset occurs.

The register fields that control the GPIO pins are described in Table 63.

For each GPIO, the selected function is determined by the GPn_FN field, where n identifies the

GPIO pin (1 to 4). The pin direction, set by GPn_DIR, must be set according to function selected by

GPn_SEL.

WM8948ECS/R Datenblatt(PDF) 97 Page - Wolfson Microelectronics plc

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