WM8311 datasheet(129/302 Pages) WOLFSON

129 / 302 page

Pre-Production

WM8311

PP, May 2012, Rev 3.1

129

19 TOUCH PANEL CONTROLLER

19.1 GENERAL DESCRIPTION

The WM8311 incorporates a Touch Panel controller interface, supporting standard resistive 4-wire

and 5-wire panel types. The controller supports X, Y co-ordinate measurement and Pen Down

detection. The 4-wire configuration also supports Touch Pressure (Z-axis) measurement.

The Touch Panel interfaces via GPIO pins 13-16. (In 5-wire mode, the AUXADCIN4 pin is also used.)

The controller provides high resolution digitiser measurements, using the same 12-bit AUXADC as

described in Section 18. Touch Panel conversion requests are interleaved with AUXADC

measurement requests.

The Touch Panel can be enabled or disabled in the SLEEP state; Pen Down detection can be used to

issue a WAKE request, including when the Touch Panel is disabled.

Touch Panel Interrupts can be generated on completion of a set of measurements, or on Pen Down

detection. Read access to the Touch Panel measurement data is controlled in order to ensure the

host always reads a complete set of data, and does not read mixed data that relates to separate

measurement events.

An overview of Touch Panel operating principles is provided in Section 19.6.

19.2 TOUCH PANEL CONFIGURATION

The Touch Panel interface uses GPIO pins 13-16. When the Touch Panel is enabled, the GPIO

functionality on these pins must be disabled by tri-stating the GPIO using the GPn_ENA register bits

(see Section 21.3).

When the Touch Panel is enabled, then TPVDD should be connected to the LDO13VOUT (INTVDD)

power domain. It is important that TPVDD is not connected to a higher voltage than this. Note that,

due to the ratiometric measurement method, the accuracy of the supply voltage does not affect the

measurement accuracy.

The 5-wire Touch Panel interface also uses the AUXADCIN4 pin; in this case, the AUXADCIN4 input

is not available to the AUXADC function.

The Touch Panel pin configuration differs between 4-wire and 5-wire modes as follows:

PIN NAME

4-WIRE FUNCTION

5-WIRE FUNCTION

GPIO13

Right contact

Bottom Right contact

GPIO14

Top contact

Top Right contact

GPIO15

Left contact

Top Left contact

GPIO16

Bottom contact

Bottom Left contact

AUXADCIN4

n/a

Wiper Contact

Table 69 Touch Panel Pin Configuration

The Touch Panel 4-wire or 5-wire mode is selected using the TCH_5WIRE bit.

Pressure measurement (4-wire mode only) uses a constant current source to measure the resistance

between the top and bottom sheets of the touch panel. The current is selectable using TCH_ISEL, to

suit different types of touch panel.

Pen Down detection sensitivity can be controlled using TCH_RPU. Decreasing the resistance makes

the touch panel less sensitive; increasing the resistance makes the touch panel more sensitive.

The Touch Panel configuration register bits are defined in Table 70.

WM8311 Datasheet(PDF) 129 Page - Wolfson Microelectronics plc

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