WM9715L
Production Data
When COO is ‘0’, the WM9715L performs one type of measurement once (in polling mode) or
continuously (in continuous mode).
The co-ordinate mode (COO = ‘1’) makes it easier to obtain co-ordinate pairs rather than single co-
ordinates. In polling-coordinate mode (CTC = ‘0’, COO = ‘1’), the WM9715L performs an X
measurement, followed by a Y measurement, followed by an additional measurement determined by
ADCSEL, then stops. In continuous-coordinate mode (CTC = ‘1’, COO = ‘1’), the WM9715L
continuously repeats a sequence consisting of an X-co-ordinate measurement, followed by a Y co-
ordinate measurement, followed by an additional measurement determined by ADCSEL (if ADCSEL
= 000, the sequence is XYXYXY… only).
DATA READBACK
The output data word of the touchpanel interface consists of three parts:
•
Pen Status (1 bit) – this is also passed to the interrupt logic block, which can be
programmed to generate an interrupt and/or wake up the WM9715L on pen down (see
“Interrupt Control”).
•
Output data from the touchpanel ADC (12 bits)
•
ADCSRC: 3 additional bits that indicate the source of the ADC data. With COO = ‘0’,
ADCSRC echoes ADCSEL. However, in co-ordinate mode (COO = ‘1’), the WM9715L
schedules different types of measurements autonomously and sets the ADCSRC bits
accordingly (see “Measurement Types”).
This data is stored in register 7Ah, and can be retrieved by reading the register in the usual manner
(see AC-Link Interface section). Additionally, the data can also be passed to the controller on one of
the AC-Link time slots not used for audio functions.
To minimize CPU loading, it is recommended to use interrupt-driven methods rather than polling
routines for reading touchpanel data. However, where polling routines are used, two methods are
available for determining when a measurement has finished:
•
•
Reading back the POLL bit. If it has been reset to ‘0’, then the measurement has finished.
Reading back 7Ah until the new data appears
REGISTER
ADDRESS
BIT
15
LABEL
PNDN
DEFAULT
DESCRIPTION
Pen status (read-only)
7Ah
or
0
0: Pen Up
AC-Link slot
selected by
SLT
1: Pen Down
14:12
ADCSRC
000
Touchpanel ADC Source
000: No measurement
001: X co-ordinate measurement
010: Y co-ordinate measurement
011: Pressure measurement
(4-wire touchpanels only)
100: COMP1/AUX1 measurement (pin 29)
101: COMP2/AUX2 measurement (pin 30)
110: BMON/AUX3 measurement (pin 31)
111: WIPER/AUX4 measurement (pin 12)
Touchpanel ADC Data (read-only)
Bit 11 = MSB
11:0
9
ADCD
WAIT
000h
0
Bit 0 = LSB
78h
0: No effect (new ADC data overwrites
unread data in register 7Ah)
1: New data is held back, and
measurements delayed, until register 7Ah is
read)
Table 27 Touchpanel Digitiser Data
To avoid losing data that has not yet been read, the WM9715L can delay overwriting register 7Ah
with new data until the old data has been read. This function is enabled using the WAIT bit.
PD Rev 4.0 December 2007
44
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
