WM8311 datasheet(133/302 Pages) WOLFSON

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WM8311

PP, May 2012, Rev 3.1

133

19.5 TOUCH PANEL INTERRUPTS

Touch panel events are associated with two Interrupt event flags.

The TCHDATA_EINT interrupt bit is set when new Touch Panel data is available. This secondary

interrupt triggers a primary Interrupt, TCHDATA_INT (see Section 23). This can be masked by setting

the IM_TCHDATA_EINT mask bit as described in Table 73.

The TCHPD_EINT interrupt bit is set when a Touch Panel ‘Pen Down’ event is detected. This

secondary interrupt triggers a primary Interrupt, TCHPD_INT (see Section 23). This can be masked

by setting the IM_TCHPD_EINT mask bit as described in Table 73.

ADDRESS

BIT

LABEL

DESCRIPTION

R16401

(4011h)

Interrupt Status

TCHDATA_EINT

Touch panel Data interrupt

(Rising Edge triggered)

Note: Cleared when a ‘1’ is written.

TCHPD_EINT

Touch panel Pen Down interrupt

(Rising Edge triggered)

Note: Cleared when a ‘1’ is written.

R16409

(4019h)

Interrupt Status

1 Mask

IM_TCHDATA_EINT

Interrupt mask.

0 = Do not mask interrupt.

1 = Mask interrupt.

Default value is 1 (masked)

IM_TCHPD_EINT

Interrupt mask.

0 = Do not mask interrupt.

1 = Mask interrupt.

Default value is 1 (masked)

Table 73 Touch Panel Interrupts

19.6 TOUCH PANEL OPERATING PRINCIPLES

A typical resistive Touch Panel comprises two conductive sheets, connected via a switch matrix to the

Touch Panel supply voltage. When the Touch Panel is touched (usually with a pen-style pointer), an

electrical contact is made between the two sheets. The switch matrix is used to determine the position

of the pen contact by establishing a potential divider on one of the conductive sheets in either the X-

axis or Y-axis, and measuring the voltage on the other sheet.

Separate configuration is required for each axis measurement; these are configured one after the

other to determine the X and Y co-ordinate positions. Note that, due to the ratiometric measurement

method, the accuracy of the supply voltage does not affect the measurement accuracy in either axis.

Pen Down detection and Z-axis (pressure) measurements are achieved in a similar fashion, by

configuring the switch matrix and taking the appropriate voltage measurement via an ADC. Note that

Z-axis measurement is only supported in 4-wire configuration.

The standard operating principles of 4-wire and 5-wire Touch Panels are each described in the

following pages.

19.6.1 4-WIRE TOUCH PANEL OPERATION

In 4-wire operation, the Touch Panel interface connects to the Left / Right sides of one sheet and to

the Top / Bottom sides of the other sheet. The illustrations show the top sheet for X-axis and the

bottom sheet for Y-axis, but the reverse is also possible.

X-axis measurement is performed by applying a potential difference between the Left and Right sides

of the touch panel. When contact is made between the two sheets, the voltage present on the Top or

Bottom connections is a measure of the X-axis position of the contact. The configuration is illustrated

in Figure 28.

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