WM8945
Production Data
DESCRIPTION
REGISTER
ADDRESS
BIT
LABEL
DEFAULT
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.
REGISTER
ADDRESS
BIT
LABEL
TCH_PD1
DEFAULT
DESCRIPTION
R57 (39h)
Pen down status (indicates if the
Pen Down was detected prior to the
TP measurement)
15
0
Touch Data X
0 = Pen Down not detected
1 = Pen Down detected
Touch panel X-axis data
TCH_X [11:0]
TCH_PD2
11:0
15
000h
0
R58 (3Ah)
Pen down status (indicates if the
Pen Down was detected prior to the
TP measurement)
Touch Data Y
0 = Pen Down not detected
1 = Pen Down detected
Touch panel Y-axis data
TCH_Y [11:0]
TCH_PD3
11:0
15
000h
0
R59 (3Bh)
Pen down status (indicates if the
Pen Down was detected prior to the
TP measurement)
Touch Data Z
0 = Pen Down not detected
1 = Pen Down detected
Touch panel Z-axis data
TCH_Z [11:0]
11:0
000h
Table 60 Touch Panel Readback
PD, May 2011, Rev 4.1
88
w
WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
