WM8945 datasheet(86/169 Pages) WOLFSON

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WM8945

Production Data

PD, May 2011, Rev 4.1

In a typical application, it is anticipated that the AUXADC Interrupt or GPIO flag would be used to

control the AUXADC readback – the host processor should read the AUXADC Data Register in

response to the AUXADC event. In Automatic AUXADC mode, the processor should complete this

action before the next measurement occurs, in order to avoid losing any AUXADC samples. In

Manual conversion mode, the interrupt signal provides confirmation that the commanded

measurement has been completed.

The control fields associated with AUXADC readback are defined in Table 58.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R60 (3Ch)

Aux ADC Data

13:12

AUX_DATA_

SRC [1:0]

AUXADC Data Source

00 = No measurement

01 = AUX1

10 = AUX2

11 = SPKVDD

11:0

AUX_DATA

[11:0]

000h

AUXADC data

(12 bit unsigned data)

Table 58 AUXADC Readback

TOUCH PANEL CONTROLLER

The WM8945 incorporates a Touch Panel controller interface, for use with standard 4-wire Touch

Panels. The controller supports X, Y co-ordinate measurement, Pen Down detection and Touch

Pressure (Z-axis) measurement.

The Touch Panel controller provides high resolution digitiser measurements, using the same 12-bit

AUXADC as described earlier (see “Auxiliary ADC”). Touch Panel conversion requests are

interleaved with AUXADC measurement requests.

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 at the end of this section.

TOUCH PANEL CONTROL

The Touch Panel is enabled by setting the TCH_ENA register bit.

The Touch Panel measurements can be initiated manually or automatically. For automatic operation,

the TCH_RATE register is set according to the required conversion rate, and measurements are

enabled by setting the TCH_CVT_ENA bit. For manual operation, the TCH_RATE register is set to

00h, and a set of measurements is initiated by setting the TCH_CVT_ENA bit. In manual mode, the

TCH_CVT_ENA bit is reset by the WM8945 after each conversion request.

The Touch Panel ‘Pen Down’ detection can be used to control measurements in automatic mode.

When TCH_PDONLY is set, then automatic conversions will only be scheduled when ‘Pen Down’ is

detected. Note that manual conversion commands are not affected by TCH_PDONLY.

For each Touch Panel measurement event (in Manual or Automatic modes), the WM8945 performs a

set of measurements encompassing all enabled input sources; the X-axis, Y-axis and Z-axis

measurements are enabled using the TCH_X_ENA, TCH_Y_ENA and TCH_Z_ENA register bits

respectively. To allow settling time between consecutive measurements, a programmable delay is

applied between the X, Y and Z-axis measurements; this is set using the TCH_DELAY field.

Pressure measurement 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 control fields associated with initiating Touch Panel measurements are defined in Table 59.

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