WM8945ECSSLASHR datasheet(88/169 Pages) WOLFSON

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WM8945

Production Data

PD, May 2011, Rev 4.1

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

3:0

TCH_RPU [3:0]

0111

Pen-Down sensitivity (pull-up

resistor)

0000 = 64k (most sensitive)

0001 = 64k / 2

0010 = 64k / 3

0011 = 64k / 4

….

1111 = 64k / 16 (least sensitive)

Table 59 Touch Panel Control

TOUCH PANEL READBACK

Measured data from the Touch Panel controller is read via the Touch Data registers. The X-axis, Y-

axis and Z-axis (pressure) measurements are provided in the TCH_X, TCH_Y and TCH_Z registers

respectively. The TCH_PD1, TCH_PD2 and TCH_PD3 bits indicate whether the Pen Down status

was asserted when the measurement set was made.

To read a set of Touch Panel measurements, the host processor must access each of the applicable

Touch Data registers. When the host processor starts to read these registers, the WM8945 will inhibit

any new touch panel measurements until the host processor has read all of the applicable registers.

This ensures that the data read by the host processor all relates to the same set of measurements.

If all 3 touch panel channels are selected (using TCH_X_ENA, TCH_Y_ENA and TCH_Z_ENA) then

all 3 Touch Data registers must be read before further measurements are permitted. If fewer channels

are selected, then only those selected channels need to be read before touch panel measurements

are enabled again.

The touch panel inhibit (preventing new touch panel measurements) commences when any of the

Touch Data registers is read. The touch panel inhibit ceases when all selected Touch Data registers

have been read.

The Touch Panel interrupts can be used to indicate when new data is available or if “Pen Down” is

detected – see “Interrupts”. A GPIO pin configured as “TCH_DONE” or “PDOWN” can also be used to

indicate these events – see “General Purpose Input / Output”.

The control fields associated with Touch Panel readback are defined in Table 60.

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R57 (39h)

Touch Data X

TCH_PD1

Pen down status (indicates if the

Pen Down was detected prior to the

TP measurement)

0 = Pen Down not detected

1 = Pen Down detected

11:0

TCH_X [11:0]

000h

Touch panel X-axis data

R58 (3Ah)

Touch Data Y

TCH_PD2

Pen down status (indicates if the

Pen Down was detected prior to the

TP measurement)

0 = Pen Down not detected

1 = Pen Down detected

11:0

TCH_Y [11:0]

000h

Touch panel Y-axis data

R59 (3Bh)

Touch Data Z

TCH_PD3

Pen down status (indicates if the

Pen Down was detected prior to the

TP measurement)

0 = Pen Down not detected

1 = Pen Down detected

11:0

TCH_Z [11:0]

000h

Touch panel Z-axis data

Table 60 Touch Panel Readback

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