WM8311 Datasheet, PDF (133/302 Pages) Wolfson Microelectronics plc – Processor Power Management Subsystem

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WM8311
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
R16401
(4011h)
Interrupt Status
1
BIT
LABEL
10 TCHDATA_EINT
9
TCHPD_EINT
R16409
(4019h)
Interrupt Status
1 Mask
10 IM_TCHDATA_EINT
9
IM_TCHPD_EINT
Table 73 Touch Panel Interrupts
DESCRIPTION
Touch panel Data interrupt
(Rising Edge triggered)
Note: Cleared when a ‘1’ is written.
Touch panel Pen Down interrupt
(Rising Edge triggered)
Note: Cleared when a ‘1’ is written.
Interrupt mask.
0 = Do not mask interrupt.
1 = Mask interrupt.
Default value is 1 (masked)
Interrupt mask.
0 = Do not mask interrupt.
1 = Mask interrupt.
Default value is 1 (masked)
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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PP, May 2012, Rev 3.1
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